[clang] [llvm] [X86] Add "Ws" constraint and "p" modifier for symbolic address/label reference (PR #77886)

[Fangrui Song via cfe-commits]

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@@ -5336,6 +5336,7 @@ X86:
   operand in a SSE register. If AVX is also enabled, can also be a 256-bit
   vector operand in an AVX register. If AVX-512 is also enabled, can also be a
   512-bit vector operand in an AVX512 register. Otherwise, an error.
+- ``Ws``: A symbolic reference or label reference.
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MaskRay wrote:

x86 has almost run out of uppercase and lowercase letters... The remaining ones are `z` and `H`.

I tried `z` but one GCC x86 maintainer considers `W` prefix better: https://gcc.gnu.org/pipermail/gcc-patches/2024-January/642596.html

https://github.com/llvm/llvm-project/pull/77886