[PowerPC] [Clang] Port SSE2 intrinsics to PowerPC

Port emmintrin.h which include Intel SSE2 intrinsics implementation to PowerPC platform (using Altivec).

The new headers containing those implemenations are located into a directory named ppc_wrappers
which has higher priority when the platform is PowerPC on Linux. They are mainly developed by Steven Munroe,
with contributions from Paul Clarke, Bill Schmidt, Jinsong Ji and Zixuan Wu.

It's a follow-up patch of D62121.

Patched by: Qiu Chaofan <qiucf@cn.ibm.com>

Differential Revision: https://reviews.llvm.org/D62569

llvm-svn: 363122

clang/lib/Headers/CMakeLists.txt

@@ -131,6 +131,7 @@ set(ppc_wrapper_files
   ppc_wrappers/mmintrin.h
   ppc_wrappers/xmmintrin.h
   ppc_wrappers/mm_malloc.h
+  ppc_wrappers/emmintrin.h
 )
 
 set(openmp_wrapper_files

clang/test/Headers/ppc-sse2-intrinsics.c

@@ -0,0 +1,14 @@
+// NOTE: Assertions have been autogenerated by utils/update_cc_test_checks.py
+// REQUIRES: powerpc-registered-target
+
+// RUN: %clang -target powerpc64-unknown-linux-gnu -S -emit-llvm -mcpu=pwr8 -DNO_WARN_X86_INTRINSICS %s -Xclang -verify
+// RUN: %clang -target powerpc64le-unknown-linux-gnu -S -emit-llvm -mcpu=pwr8 -DNO_WARN_X86_INTRINSICS %s -Xclang -verify -x c++
+// expected-no-diagnostics
+
+// RUN: not %clang -target powerpc64-unknown-linux-gnu -S -emit-llvm %s -mcpu=pwr8 -o /dev/null 2>&1 | FileCheck %s -check-prefix=SSE2-ERROR
+
+// Don't include mm_malloc.h, it's system specific.
+#define _MM_MALLOC_H_INCLUDED
+
+#include <emmintrin.h>
+// SSE2-ERROR: xmmintrin.h:{{[0-9]+}}:{{[0-9]+}}: error: "Please read comment above. Use -DNO_WARN_X86_INTRINSICS to disable this error."