[clang] InterpBuiltin - replace interp__builtin_elementwise_popcount with interp__builtin_elementwise_int_unaryop callback

[RKSimon]

• Extend interp__builtin_elementwise_int_unaryop to handle vectors
• Replace BI__builtin_elementwise_popcount with interp__builtin_elementwise_int_unaryop callback.
• Replace BI__builtin_elementwise_bitreverse with interp__builtin_elementwise_int_unaryop callback.
• Remove interp__builtin_elementwise_popcount

[llvmbot]

Hi!

This issue may be a good introductory issue for people new to working on LLVM. If you would like to work on this issue, your first steps are:

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3. Fix the issue locally.
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[llvmbot]

@llvm/issue-subscribers-good-first-issue

Author: Simon Pilgrim (RKSimon)

- Extend interp__builtin_elementwise_int_unaryop to handle vectors - Replace with BI__builtin_elementwise_popcount with interp__builtin_elementwise_int_unaryop callback. - Replace with BI__builtin_elementwise_bitreverse with interp__builtin_elementwise_int_unaryop callback. - Remove interp__builtin_elementwise_popcount

[Islam-Imad]

Hi Simon! Hope you're doing well.
Could you assign this issue to me, please :) ?