[clang] [llvm] [X86] Accept 'a' modifier for 'p' constraint in inline asm (PR #185590)

[Fangrui Song via cfe-commits]

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MaskRay wrote:

`i` and `r` constraints use `PrintAsmOperand` instead of `PrintAsmMemoryOperand`. This patch only changes `PrintAsmMemoryOperand`, so `i` and `r` constraints are still allowed.

https://github.com/llvm/llvm-project/pull/185590