This adds support for:
* `muslabin32` (MIPS N32)
* `muslabi64` (MIPS N64)
* `muslf32` (LoongArch ILP32F/LP64F)
* `muslsf` (LoongArch ILP32S/LP64S)
As we start adding glibc/musl cross-compilation support for these
targets in Zig, it would make our life easier if LLVM recognized these
triples. I'm hoping this'll be uncontroversial since the same has
already been done for `musleabi`, `musleabihf`, and `muslx32`.
I intentionally left out a musl equivalent of `gnuf64` (LoongArch
ILP32D/LP64D); my understanding is that Loongson ultimately settled on
simply `gnu` for this much more common case, so there doesn't *seem* to
be a particularly compelling reason to add a `muslf64` that's basically
deprecated on arrival.
Note: I don't have commit access.
72a218056d