[PowerPC][Power10] Implement Count Leading/Trailing Zeroes Builtins under bit Mask...

[PowerPC][Power10] Implement Count Leading/Trailing Zeroes Builtins under bit Mask in LLVM/Clang

This patch implements builtins for the following prototypes:

unsigned long long __builtin_cntlzdm (unsigned long long, unsigned long long)
unsigned long long __builtin_cnttzdm (unsigned long long, unsigned long long)
vector unsigned long long vec_cntlzm (vector unsigned long long, vector unsigned long long)
vector unsigned long long vec_cnttzm (vector unsigned long long, vector unsigned long long)

Differential Revision: https://reviews.llvm.org/D80941