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..004dc66bc9554c34f674f61b692d7fd788d859c5 100644
--- a/src/IceTargetLowering.cpp
+++ b/src/IceTargetLowering.cpp
@@ -230,7 +230,7 @@ void TargetLowering::lower() {
 // registers e.g. for performance testing.
 void TargetLowering::regAlloc() {
   static TimerIdT IDregAlloc = GlobalContext::getTimerID("regAlloc");
-  TimerMarker T(IDregAlloc, Ctx);
+  TimerMarker T(IDregAlloc, Func);
   LinearScan LinearScan(Func);
   RegSetMask RegInclude = RegSet_None;
   RegSetMask RegExclude = RegSet_None;