[clang] added regcall struct by reg support (PR #95257)

[via cfe-commits]

mahesh-attarde wrote:

Regcall ABI is described on  https://cdrdv2-public.intel.com/679047/Intel-ABI-Vector-Function-v0.9.8.pdf 
Page No. 18

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![image](https://github.com/llvm/llvm-project/assets/145317060/5ff49ca5-0b4c-4c8f-9f00-5de65e4eaeda)


https://github.com/llvm/llvm-project/pull/95257