Remove requirement for -maltivec to be used when using -mabi=vec-extabi or...

Remove requirement for -maltivec to be used when using -mabi=vec-extabi or -mabi=vec-default when not using vector code

The previous implementation required that `-maltivec` be specified when using either `-mabi=vec-extabi` or `-mabi=vec-default`, this patch removes that requirement.

Reviewed By: cebowleratibm

Differential Revision: https://reviews.llvm.org/D94986