dist-various-2: Use clang for the UEFI targets

dist-various-2: Use clang for the UEFI targets

This fixes an issue where the C and asm sources built by
compiler_builtins were being compiled as ELF objects instead of PE
objects. This wasn't noticed before because it doesn't cause
compiler_builtins or rustc to fail to build. You only see a failure when
a program is built that references one of the symbols in an ELF object.

Compiling with clang fixes this because the `cc` crate converts the UEFI
targets into Windows targets that clang understands, causing it to
produce PE objects.

Note that this requires compiler_builtins >= 0.1.84.

Fixes https://github.com/rust-lang/rust/issues/104326