Add FEAT_PCDPHINT Support

[ricbal02]

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Hi all,

This is a PR to propose the addition of new intrinsics required as part of FEAT_PCDPHINT.

I'm very open to suggestions on potential improvements and certainly not overly committed to the current name.
This will need approval from LLVM as well.

Quality Level: ALP

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[Wilco1]

x

[ricbal02]

Hi all, I now have a GCC patch for this in Upstream review. Would I be able to get some final approval/review on this ACLE patch. Thanks

[jthackray]

LGTM