Firestore: pin googletest to a commit that supports c++14 in cmake builds

[dconeybe]

Before this PR, Firestore's cmake build always built against the main branch of https://github.com/google/googletest:

firebase-ios-sdk/cmake/external/googletest.cmake

Line 23 in bbd9fb3

set(version main)

This worked fine, until googletest dropped c++14 support on Feb 10, 2025 in commit google/googletest@c00fd25. Since firebase-ios-sdk requires c++14 support, this caused all sorts of build errors (see examples below). The fix in this PR is to pin googletest at the last commit that supported c++14.

FAILED: Firestore/core/test/unit/util/CMakeFiles/firestore_util_test.dir/iterator_adaptors_test.cc.o 
/usr/bin/ccache /usr/bin/c++ -DCARES_STATICLIB -DFIREBASE_TESTS_BUILT_BY_CMAKE -DFIRESTORE_HAVE_CONFIG_DETECTED_H -DPB_ENABLE_MALLOC -DPB_FIELD_32BIT -DPB_NO_PACKED_STRUCTS=1 -I$HOME/work/ios/main/build -I$HOME/work/ios/main -I$HOME/work/ios/main/build/external/src/abseil-cpp -I$HOME/work/ios/main/Firestore/core/include -I$HOME/work/ios/main/build/external/src/leveldb/include -I$HOME/work/ios/main/build/external/src/snappy-build -I$HOME/work/ios/main/build/external/src/snappy -I$HOME/work/ios/main/build/external/src/nanopb -I$HOME/work/ios/main/Firestore/Protos/nanopb -I$HOME/work/ios/main/build/external/src/grpc/include -I$HOME/work/ios/main/build/external/src/re2 -I$HOME/work/ios/main/build/external/src/grpc-build/third_party/cares/cares -I$HOME/work/ios/main/build/external/src/cares -I$HOME/work/ios/main/build/external/src/protobuf/src -isystem $HOME/work/ios/main/build/external/src/googletest/googletest/include -isystem $HOME/work/ios/main/build/external/src/googletest/googletest -isystem $HOME/work/ios/main/build/external/src/googletest/googlemock/include -isystem $HOME/work/ios/main/build/external/src/googletest/googlemock -isystem $HOME/local/homebrew/Cellar/openssl@3/3.4.1/include -Wno-format-zero-length -g -std=gnu++17 -Wall -Wextra -Werror -Wformat -Wuninitialized -fno-common -Wunused-function -Wunused-value -Wunused-variable -fdiagnostics-color -Wno-error=redundant-move -Wreorder -Werror=reorder -MD -MT Firestore/core/test/unit/util/CMakeFiles/firestore_util_test.dir/iterator_adaptors_test.cc.o -MF Firestore/core/test/unit/util/CMakeFiles/firestore_util_test.dir/iterator_adaptors_test.cc.o.d -o Firestore/core/test/unit/util/CMakeFiles/firestore_util_test.dir/iterator_adaptors_test.cc.o -c $HOME/work/ios/main/Firestore/core/test/unit/util/iterator_adaptors_test.cc
$HOME/work/ios/main/Firestore/core/test/unit/util/iterator_adaptors_test.cc:85:41: error: ‘template<class _Category, class _Tp, class _Distance, class _Pointer, class _Reference> struct std::iterator’ is deprecated [-Werror=deprecated-declarations]
   85 |   class InlineStorageIter : public std::iterator<std::input_iterator_tag, T> {
      |                                         ^~~~~~~~
In file included from /usr/include/c++/14/iterator:61,
                 from $HOME/work/ios/main/Firestore/core/src/util/iterator_adaptors.h:22,
                 from $HOME/work/ios/main/Firestore/core/test/unit/util/iterator_adaptors_test.cc:17:
/usr/include/c++/14/bits/stl_iterator_base_types.h:127:34: note: declared here
  127 |     struct _GLIBCXX17_DEPRECATED iterator
      |                                  ^~~~~~~~
$HOME/work/ios/main/Firestore/core/test/unit/util/iterator_adaptors_test.cc:571:19: error: ‘template<class _Category, class _Tp, class _Distance, class _Pointer, class _Reference> struct std::iterator’ is deprecated [-Werror=deprecated-declarations]
  571 |     : public std::iterator<std::input_iterator_tag, const int*> {
      |                   ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator_base_types.h:127:34: note: declared here
  127 |     struct _GLIBCXX17_DEPRECATED iterator
      |                                  ^~~~~~~~
cc1plus: all warnings being treated as errors

and

FAILED: Firestore/core/test/unit/local/firestore_local_test 
: && /usr/bin/c++ -g -Wl,--dependency-file=Firestore/core/test/unit/local/CMakeFiles/firestore_local_test.dir/link.d Firestore/core/test/unit/local/CMakeFiles/firestore_local_test.dir/bundle_cache_test.cc.o Firestore/core/test/unit/local/CMakeFiles/firestore_local_test.dir/document_overlay_cache_test.cc.o Firestore/core/test/unit/local/CMakeFiles/firestore_local_test.dir/globals_cache_test.cc.o Firestore/core/test/unit/local/CMakeFiles/firestore_local_test.dir/index_backfiller_test.cc.o Firestore/core/test/unit/local/CMakeFiles/firestore_local_test.dir/index_manager_test.cc.o Firestore/core/test/unit/local/CMakeFiles/firestore_local_test.dir/leveldb_bundle_cache_test.cc.o Firestore/core/test/unit/local/CMakeFiles/firestore_local_test.dir/leveldb_document_overlay_cache_test.cc.o Firestore/core/test/unit/local/CMakeFiles/firestore_local_test.dir/leveldb_globals_cache_test.cc.o Firestore/core/test/unit/local/CMakeFiles/firestore_local_test.dir/leveldb_index_manager_test.cc.o Firestore/core/test/unit/local/CMakeFiles/firestore_local_test.dir/leveldb_key_test.cc.o Firestore/core/test/unit/local/CMakeFiles/firestore_local_test.dir/leveldb_local_store_test.cc.o Firestore/core/test/unit/local/CMakeFiles/firestore_local_test.dir/leveldb_lru_garbage_collector_test.cc.o Firestore/core/test/unit/local/CMakeFiles/firestore_local_test.dir/leveldb_migrations_test.cc.o Firestore/core/test/unit/local/CMakeFiles/firestore_local_test.dir/leveldb_mutation_queue_test.cc.o Firestore/core/test/unit/local/CMakeFiles/firestore_local_test.dir/leveldb_opener_test.cc.o Firestore/core/test/unit/local/CMakeFiles/firestore_local_test.dir/leveldb_overlay_migration_manager_test.cc.o Firestore/core/test/unit/local/CMakeFiles/firestore_local_test.dir/leveldb_query_engine_test.cc.o Firestore/core/test/unit/local/CMakeFiles/firestore_local_test.dir/leveldb_remote_document_cache_test.cc.o Firestore/core/test/unit/local/CMakeFiles/firestore_local_test.dir/leveldb_snappy_test.cc.o Firestore/core/test/unit/local/CMakeFiles/firestore_local_test.dir/leveldb_target_cache_test.cc.o Firestore/core/test/unit/local/CMakeFiles/firestore_local_test.dir/leveldb_transaction_test.cc.o Firestore/core/test/unit/local/CMakeFiles/firestore_local_test.dir/leveldb_util_test.cc.o Firestore/core/test/unit/local/CMakeFiles/firestore_local_test.dir/local_serializer_test.cc.o Firestore/core/test/unit/local/CMakeFiles/firestore_local_test.dir/local_store_test.cc.o Firestore/core/test/unit/local/CMakeFiles/firestore_local_test.dir/lru_garbage_collector_test.cc.o Firestore/core/test/unit/local/CMakeFiles/firestore_local_test.dir/memory_bundle_cache_test.cc.o Firestore/core/test/unit/local/CMakeFiles/firestore_local_test.dir/memory_document_overlay_cache_test.cc.o Firestore/core/test/unit/local/CMakeFiles/firestore_local_test.dir/memory_globals_cache_test.cc.o Firestore/core/test/unit/local/CMakeFiles/firestore_local_test.dir/memory_index_manager_test.cc.o Firestore/core/test/unit/local/CMakeFiles/firestore_local_test.dir/memory_local_store_test.cc.o Firestore/core/test/unit/local/CMakeFiles/firestore_local_test.dir/memory_lru_garbage_collector_test.cc.o Firestore/core/test/unit/local/CMakeFiles/firestore_local_test.dir/memory_mutation_queue_test.cc.o Firestore/core/test/unit/local/CMakeFiles/firestore_local_test.dir/memory_query_engine_test.cc.o Firestore/core/test/unit/local/CMakeFiles/firestore_local_test.dir/memory_remote_document_cache_test.cc.o Firestore/core/test/unit/local/CMakeFiles/firestore_local_test.dir/memory_target_cache_test.cc.o Firestore/core/test/unit/local/CMakeFiles/firestore_local_test.dir/mutation_queue_test.cc.o Firestore/core/test/unit/local/CMakeFiles/firestore_local_test.dir/query_engine_test.cc.o Firestore/core/test/unit/local/CMakeFiles/firestore_local_test.dir/reference_set_test.cc.o Firestore/core/test/unit/local/CMakeFiles/firestore_local_test.dir/remote_document_cache_test.cc.o 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/usr/bin/ld: Firestore/core/test/unit/local/CMakeFiles/firestore_local_test.dir/globals_cache_test.cc.o: in function `firebase::firestore::local::(anonymous namespace)::GlobalsCacheTest_ReturnsSavedSessionToken_Test::TestBody()::{lambda()#1}::operator()() const':
$HOME/work/ios/main/Firestore/core/test/unit/local/globals_cache_test.cc:52:(.text+0x9e1): undefined reference to `firebase::firestore::nanopb::ByteString::ByteString(std::basic_string_view<char, std::char_traits<char> >)'
/usr/bin/ld: $HOME/work/ios/main/Firestore/core/test/unit/local/globals_cache_test.cc:59:(.text+0xb57): undefined reference to `firebase::firestore::nanopb::ByteString::ByteString(std::basic_string_view<char, std::char_traits<char> >)'
/usr/bin/ld: Firestore/core/test/unit/local/CMakeFiles/firestore_local_test.dir/leveldb_key_test.cc.o: in function `firebase::firestore::local::(anonymous namespace)::DocMutationKey(std::basic_string_view<char, std::char_traits<char> >, std::basic_string_view<char, std::char_traits<char> >, int)':
$HOME/work/ios/main/Firestore/core/test/unit/local/leveldb_key_test.cc:50:(.text+0x17a): undefined reference to `firebase::firestore::local::LevelDbDocumentMutationKey::Key[abi:cxx11](std::basic_string_view<char, std::char_traits<char> >, firebase::firestore::model::DocumentKey const&, int)'
/usr/bin/ld: Firestore/core/test/unit/local/CMakeFiles/firestore_local_test.dir/leveldb_key_test.cc.o: in function `firebase::firestore::local::(anonymous namespace)::RemoteDocumentReadTimeKey(std::basic_string_view<char, std::char_traits<char> >, long, std::basic_string_view<char, std::char_traits<char> >)':

#no-changelog

[paulb777]

Thanks @dconeybe !