[X86] Replace SSE mulh target intrinsics with generics

Once #220293 has landed we can remove the (V)PMULHW + (V)PMULHUW x86 intrinsics and use the llvm.[su]mulh intrinsics directly:

- [ ] Move the `llvm.x86.*.pmulh.w` and `llvm.x86.*.pmulhu.w` intrinsic codegen to the *-intrinsics-upgrade.ll test files
- [ ] Handle `llvm.x86.*.pmulh.w` and `llvm.x86.*.pmulhu.w` intrinsics -> `llvm.[su]mulh` intrinsics in Autoupgrade
- [ ] Update stack folding tests to use the `llvm.[su]mulh` intrinsics directly
- [ ] clang\lib\CodeGen\TargetBuiltins\X86.cpp - emit `llvm.[su]mulh` intrinsics
- [ ] Remove `llvm.x86.*.pmulh.w` and `llvm.x86.*.pmulhu.w` intrinsic defs

First confirm that #220293 has landed, then inspect clang/lib/CodeGen/TargetBuiltins/X86.cpp and the existing *-intrinsics-upgrade.ll and stack-folding tests. Trace the Autoupgrade handling and intrinsic definitions for the listed pmulh and pmulhu operations. Done means the tests use llvm.[su]mulh, Clang emits those intrinsics, upgrade handling exists, and the old x86 intrinsic definitions are removed.

Written by the indexing model from the issue text.