Subzero: Add a few performance measurement tools.

src/IceTargetLowering.cpp

Index: src/IceTargetLowering.cpp
diff --git a/src/IceTargetLowering.cpp b/src/IceTargetLowering.cpp
index 6dc46b1339e7aaa510c90b690273a4bed5bd813a..bcc629098bf94d13ef3012fb24900f6613dfa08b 100644
--- a/src/IceTargetLowering.cpp
+++ b/src/IceTargetLowering.cpp
@@ -229,8 +229,7 @@ void TargetLowering::lower() {
 // registers could potentially be parameterized if we want to restrict
 // registers e.g. for performance testing.
 void TargetLowering::regAlloc() {
-  static TimerIdT IDregAlloc = GlobalContext::getTimerID("regAlloc");
-  TimerMarker T(IDregAlloc, Ctx);
+  TimerMarker T(TimerStack::TT_regAlloc, Func);
   LinearScan LinearScan(Func);
   RegSetMask RegInclude = RegSet_None;
   RegSetMask RegExclude = RegSet_None;