Erm, gcc and vc will never output the same binary code, I haven't done or seen this, but it must be possible to compile clang (with mingw-gcc) for use with mingw, then with that clang-cl you might stand a chance. Sticking to static libraries, helps already (with exceptions across library boundaries), using C as glue could fix the issue forever.

Another, much simpler solution is to ditch mingw and use clang-cl as your main (or support to VC) compiler. Clang can 'theoretically' compile 'anything' (bar bugs in Clang), as long as it's coded in a std that's supported by that version of clang and the code adheres to that std, including but not limited to gcc-extensions and microsoft-extensions (in addition to clang-extensions). Contrary to what Clang claims, Clang is not fast (!!!), but it generates good code and excellent (short) error messages, sometimes better (faster binary) than VC, sometimes worse than VC, it's a crap-shoot, for speed-critical code, compiling bits with VC and bits with Clang after having identified which bits work best which compiler after bench-marking, gives to absolute best result, at least at par with gcc if not better.