[clang] [llvm] [Clang][LoongArch] Add inline asm support for the `q` constraint (PR #141037)

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heiher wrote:

> What about making a test case that exerts great pressure on the register allocator to verify that `$ra` does not get accidentally handed out?

I've done that, similar to what was done in #140862

> Or if that's too fragile, if it's possible, make a variable pinned to `$ra` or `$zero` then pass it to the inline asm block with the newly added `q` constraint, to ensure a new temp gets allocated.

It doesn't seem to work. A `register` variable appears to bypass the "q" constraint, which I believe is expected.


https://github.com/llvm/llvm-project/pull/141037