[SECP256K1] Request --enable-experimental for the multiset module

Summary:
The module is advertised as experimental, but is missing the check for
`--enable-experimental` like the other experimental modules.
Also disable it by default with cmake (which is the autotools behavior),
as it is more in accordance with its experimental status.

Depends on D5429.

Test Plan:
  ../configure --enable-module-multiset
Check it fails with a message asking for --enable-experimental.

  ../configure --enable-module-multiset --enable-experimental
  make check

  cmake -GNinja .. -DSECP256K1_ENABLE_MODULE_MULTISET=ON
  ninja check-secp256k1

  cmake -GNinja ..
  ninja check-secp256k1

Run the Travis build (see https://travis-ci.org/Fabcien/secp256k1/builds/658346030).

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D5431

.travis.yml

@@ -34,18 +34,19 @@ env:
     - EXPERIMENTAL=no
     - JNI=no
     - OPENSSL_TESTS=auto
+    - MULTISET=no
   jobs:
     - SCALAR=32bit    RECOVERY=yes
-    - SCALAR=32bit    FIELD=32bit       ECDH=yes  EXPERIMENTAL=yes
+    - SCALAR=32bit    FIELD=32bit       ECDH=yes  EXPERIMENTAL=yes  MULTISET=yes
     - SCALAR=64bit
     - FIELD=64bit     RECOVERY=yes
     - FIELD=64bit     ENDOMORPHISM=yes
-    - FIELD=64bit     ENDOMORPHISM=yes  ECDH=yes EXPERIMENTAL=yes
+    - FIELD=64bit     ENDOMORPHISM=yes  ECDH=yes  EXPERIMENTAL=yes  MULTISET=yes
     - FIELD=64bit                       ASM=x86_64
     - FIELD=64bit     ENDOMORPHISM=yes  ASM=x86_64
     - FIELD=32bit     ENDOMORPHISM=yes
     - BIGNUM=no
-    - BIGNUM=no       ENDOMORPHISM=yes RECOVERY=yes EXPERIMENTAL=yes
+    - BIGNUM=no       ENDOMORPHISM=yes  RECOVERY=yes  EXPERIMENTAL=yes  MULTISET=yes
     - BIGNUM=no       STATICPRECOMPUTATION=no
     - AUTOTOOLS_TARGET=distcheck       CMAKE_TARGET=install
     - AUTOTOOLS_EXTRA_FLAGS=CPPFLAGS=-DDETERMINISTIC CMAKE_EXTRA_FLAGS=-DCMAKE_C_FLAGS=-DDETERMINISTIC

CMakeLists.txt

@@ -193,7 +193,7 @@ if(SECP256K1_ENABLE_MODULE_ECDH)
 endif()
 
 # MultiSet module
-option(SECP256K1_ENABLE_MODULE_MULTISET "Build libsecp256k1's MULTISET module" ON)
+option(SECP256K1_ENABLE_MODULE_MULTISET "Build libsecp256k1's MULTISET module" OFF)
 if(SECP256K1_ENABLE_MODULE_MULTISET)
     set(ENABLE_MODULE_MULTISET 1)
 	add_secp256k1_bench(multiset src/bench_multiset.c)

configure.ac

@@ -554,6 +554,9 @@ else
   if test x"$enable_module_ecdh" = x"yes"; then
     AC_MSG_ERROR([ECDH module is experimental. Use --enable-experimental to allow.])
   fi
+  if test x"$enable_module_multiset" = x"yes"; then
+    AC_MSG_ERROR([Multiset module is experimental. Use --enable-experimental to allow.])
+  fi
   if test x"$set_asm" = x"arm"; then
     AC_MSG_ERROR([ARM assembly optimization is experimental. Use --enable-experimental to allow.])
   fi

travis/build_autotools.sh

@@ -27,6 +27,7 @@ pushd buildautotools
   --enable-ecmult-static-precomputation=$STATICPRECOMPUTATION \
   --with-ecmult-gen-precision=$ECMULTGENPRECISION \
   --enable-module-ecdh=$ECDH \
+  --enable-module-multiset=$MULTISET \
   --enable-module-recovery=$RECOVERY \
   --enable-module-schnorr=$SCHNORR \
   --enable-jni=$JNI \

travis/build_cmake.sh

@@ -27,6 +27,7 @@ ${CMAKE_COMMAND} -GNinja .. \
   -DSECP256K1_BUILD_OPENSSL_TESTS=$OPENSSL_TESTS \
   -DSECP256K1_ECMULT_STATIC_PRECOMPUTATION=$STATICPRECOMPUTATION \
   -DSECP256K1_ENABLE_MODULE_ECDH=$ECDH \
+  -DSECP256K1_ENABLE_MODULE_MULTISET=$MULTISET \
   -DSECP256K1_ENABLE_MODULE_RECOVERY=$RECOVERY \
   -DSECP256K1_ENABLE_MODULE_SCHNORR=$SCHNORR \
   -DSECP256K1_ENABLE_JNI=$JNI \