[clang] [PowerPC] Fix use of FPSCR builtins in smmintrin.h (PR #67299)

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JeremyRand wrote:

ACK 5abcf8964394eb5124d606b00a94781147fd8f8d. I can confirm that this fixes SSE4.1 support in [ncnn](https://github.com/Tencent/ncnn) for POWER9 LE (and gives a nice 3x speedup when benchmarking ncnn, which indicates that the additional intrinsics are actually getting used). Testing was done by applying the patch to the Clang package from Fedora 38's LLVM snapshot Copr.

I didn't attempt to test POWER8.

https://github.com/llvm/llvm-project/pull/67299