[x86] Add Clang support for intrinsic __rdpmc.

This patch adds intrinsic __rdpmc to header file 'ia32intrin.h'.
Intrinsic __rdmpc can be used to read performance monitoring counters. It is
implemented as a direct call to __builtin_ia32_rdpmc.

It takes as input a value representing the index of the performance counter to
read. The value of the performance counter is then returned as a unsigned
64-bit quantity.

llvm-svn: 212053
diff --git a/clang/test/CodeGen/builtins-x86.c b/clang/test/CodeGen/builtins-x86.c
index 8443574..0f038b8 100644
--- a/clang/test/CodeGen/builtins-x86.c
+++ b/clang/test/CodeGen/builtins-x86.c
@@ -266,6 +266,7 @@
 
   tmp_i = __builtin_ia32_rdtsc();
   tmp_i = __builtin_ia32_rdtscp(&tmp_Ui);
+  tmp_LLi = __builtin_ia32_rdpmc(tmp_i);
 #ifdef USE_64
   tmp_LLi = __builtin_ia32_cvtss2si64(tmp_V4f);
 #endif