[clang] [AArch64][SME2] Add multi-vector SEL (x2, x4) ACLE builtins & intrinsics (PR #73188)

[David Sherwood via cfe-commits]

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david-arm wrote:

Should the file be renamed to acle_sme2_vector_selx2? This would make it consistent with the existing acle_sme2_vector_add.c file, which also has SVE-like instructions that only operate on SVE vectors.

https://github.com/llvm/llvm-project/pull/73188