ams: support building unit test programs on windows/linux/macos

ams: update build system to add generic-fallback support

libstratosphere: use from /atmosphere/libraries

Improve exception wrapping

Results: Implement namespaced, type-safe results. ...

Because I was working on multiple things at once, this commit also:
- Adds wrappers for/linker flags to wrap CXX exceptions to make them
  abort. This saves ~0x8000 of memory in every system module.
- Broadly replaces lines of the pattern if (cond) { return ResultX; }
  with R_UNLESS(!cond, ResultX());.
- Reworks the R_TRY_CATCH macros (and the result macros in general).

Merge fs.mitm and set.mitm.