Add a function attribute to include in EXCEPTION_CATCHING_ALLOWED list

[tangobravo]

Managing large codebases including third-party libraries with a single global -sEXCEPTION_CATCHING_ALLOWED list is challenging from a build system perspective. It's also not that easy to find the mangled names and with C++ unnamed namespaces I think there might not even be consistent function names between build machines.

Could a function attribute be added so this could be maintained directly in the source? I'm thinking it would be similar to how EMSCRIPTEN_KEEPALIVE can be used alongside -sEXPORTED_FUNCTIONS as both are useful in different circumstances.

[kripken]

Is the standard noexcept not enough for this? (it is not the same, but maybe you can find the proper places to apply it to achieve similar results)