[PowerPC] Support for vector bool int128 on vector comparison builtins

This patch implements support for the type vector bool int128
for arguments on vector comparison builtins listed below,
which would otherwise crash due to ambiguity.

The following builtins are added:

vec_all_eq (vector bool __int128, vector bool __int128)
vec_all_ne (vector bool __int128, vector bool __int128)
vec_any_eq (vector bool __int128, vector bool __int128)
vec_any_ne (vector bool __int128, vector bool __int128)
vec_cmpne(vector bool __int128 a, vector bool __int128 b)
vec_cmpeq(vector bool __int128 a, vector bool __int128 b)

Differential revision: https://reviews.llvm.org/D110084