[PowerPC] Implement vector float and vector double version for vec_orc builtin

The builtin for vec_orc has support for the following two signatures,
but currently the compiler marks it ambiguous:
vector float vec_orc(vector float, vector float)
vector double vec_orc(vector double, vector double)

This patch implements these two builtins.

Differential revision: https://reviews.llvm.org/D110858