[clang] [llvm] [clang][uefi] add arm, aarch64, x86, loongarch64, riscv64 targets (PR #136247)

[Tristan Ross via llvm-commits]

RossComputerGuy wrote:

2 targets have complications which require non-trivial backend work:

- armv7l-unknown-uefi-llvm
- i386-unknown-uefi-llvm

There's 3 options:

1. Gut from this PR
2. Keep as it
3. Keep but mark as unsupported

https://github.com/llvm/llvm-project/pull/136247