Fix g++-10 link issue when building with -std=c++20.

[greg7mdp]

Within libraries/wasm-jit/Source, WASM depends on IR and Logging, and IR depends on Logging.
With the current declaration of WASM::check_limits in WASM, we have the following g++-10 link error when building with -std=c++20:

_64-linux-gnu/libz.so  -ldl  libraries/libfc/secp256k1/libsecp256k1.a  libraries/chainbase/libchainbase.a  -lpthread  libraries/softfloat/libsoftfloat.a && :
/usr/bin/ld: libraries/wasm-jit/Source/IR/libIR.a(DisassemblyNames.cpp.o): warning: relocation against `_ZN4WASM12check_limitsE' in read-only section `.text'
/usr/bin/ld: libraries/wasm-jit/Source/IR/libIR.a(DisassemblyNames.cpp.o): in function `void Serialization::serialize<Serialization::MemoryInputStream>(Serialization::MemoryInputStream&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >&)':
/home/greg/github/enf/leap/libraries/wasm-jit/Include/Inline/Serialization.h:274: undefined reference to `WASM::check_limits'
/usr/bin/ld: warning: creating DT_TEXTREL in a PIE
collect2: error: ld returned 1 exit status

Moving the declaration of WASM::check_limits in Logging (end leaf of dependency graph) fixes the issue.

[heifner]

Did you consider using an inline static of a struct instead? Seems like that would be cleaner than extern.

[greg7mdp]

I tried to do the minimal change to fix the issue. In my first attempt I had changed it to a function accessing a static variable, but there were more changes and I tried to find the simplest fix.

[greg7mdp]

I do like the idea of an inline static struct member, as it relies on a C++ feature that I feel should be more foolproof. Still since it is not my code, and this is a workaround for a specific compiler issue, I'd prefer to keep the change as minimal as possible.

[spoonincode]

It seems a little strange putting something that has nothing to do with logging in the Logging library. Could it work in IR instead? The Logging library could easily be on the chopping block whenever someone has time to keep trimming down WAVM.

[greg7mdp]

Thanks Matt, it looks like it is working fine with the variable in IR. I'll push that change.