Add official 64-bit LoongArch builds

[alexrp]

Support was added in glibc 2.36: https://sourceware.org/pipermail/libc-alpha/2022-August/141193.html

Should include both loongarch64-linux-gnu and loongarch64-linux-musl.

Requires:

• loongarch64 half (f16) failure to select with +f and +d llvm/llvm-project#93894

[alexrp]

This can be done in Zig 0.14.0.