ARM: Add Performance Monitor Extensions feature

Performance monitors, including a basic cycle counter, are an official
extension in the ARMv7 specification. This adds support for enabling and
disabling them, orthogonally from CPU selection.

rdar://problem/13939186

llvm-svn: 182602
diff --git a/llvm/lib/Target/ARM/ARMSubtarget.cpp b/llvm/lib/Target/ARM/ARMSubtarget.cpp
index c7d9743..455fe1a 100644
--- a/llvm/lib/Target/ARM/ARMSubtarget.cpp
+++ b/llvm/lib/Target/ARM/ARMSubtarget.cpp
@@ -106,6 +106,7 @@
   HasRAS = false;
   HasMPExtension = false;
   FPOnlySP = false;
+  HasPerfMon = false;
   HasTrustZone = false;
   AllowsUnalignedMem = false;
   Thumb2DSP = false;