(from SERVER-95407 silence and fix individual warnings from GCC 14.2)

The current split among compiler.h, compiler_gcc.h, compiler_msvc.h make it very difficult to document and maintain the MONGO_COMPILER macros, and it's a noisy way to do what it's doing. It's exhausting to jump between files to see what the same line of code might do on different compilers.

We could just have one file with appropriate #ifdef/#else/#endif blocks, and features would each be contained to one rather ordinary block of code, with a single discoverable point of documentation.