[PowerPC] [Clang] Port SSE3, SSSE3 and SSE4 intrinsics to PowerPC

Port existing headers which include x86 intrinsics implementation to
PowerPC platform (using Altivec), along with tests. Also, tests about
including these intrinsic headers are combined.

The headers are mainly developed by Steven Munroe, with contributions
from Paul Clarke, Bill Schmidt, Jinsong Ji and Zixuan Wu.

Reviewed By: Jinsong Ji

Differential Revision: https://reviews.llvm.org/D65630

llvm-svn: 368392