[clang] [Driver] Remove a bunch of unnecessary REQUIRES constraints (PR #94055)

[Fangrui Song via cfe-commits]

MaskRay wrote:

> Looks like the buildbots' -DDEFAULT_SYSROOT strikes again (boo...). I think adding --sysroot="" is a common way to handle this for tests.

I think `DEFAULT_SYSROOT` should be phased out. Downstream users can customize CMake `DEFAULT_SYSROOT` to set the default `--sysroot=`, but there should be no expectation that all tests will pass https://reviews.llvm.org/D158218.

A CMake change can be made to let `DEFAULT_SYSROOT` install `$default_triple.cfg` beside `clang` and issue a deprecation warning.
Unfortunately, WebAssembly/wasi-sdk has a reliance on this behavior https://reviews.llvm.org/D76653 https://github.com/WebAssembly/wasi-sdk/pull/171
@sunfishcode @sbc100


https://github.com/llvm/llvm-project/pull/94055