[llvm-mca] Simplify eventing by adding an onEvent templated method.

Summary:
This patch eliminates some redundancy in iterating across Listeners for the
Instruction and Stall HWEvents, by introducing a template onEvent routine.
This change was suggested by @courbet in https://reviews.llvm.org/D48576.  I
 hope that this patch addresses that suggestion appropriately.  I do like this
change better than what we had previously.


Reviewers: andreadb, courbet, RKSimon

Reviewed By: andreadb, courbet

Subscribers: javed.absar, tschuett, gbedwell, llvm-commits, courbet

Differential Revision: https://reviews.llvm.org/D48672

llvm-svn: 336916
diff --git a/llvm/tools/llvm-mca/RetireControlUnitStatistics.cpp b/llvm/tools/llvm-mca/RetireControlUnitStatistics.cpp
index 5d3632f..edb855e 100644
--- a/llvm/tools/llvm-mca/RetireControlUnitStatistics.cpp
+++ b/llvm/tools/llvm-mca/RetireControlUnitStatistics.cpp
@@ -19,8 +19,7 @@
 
 namespace mca {
 
-void RetireControlUnitStatistics::onInstructionEvent(
-    const HWInstructionEvent &Event) {
+void RetireControlUnitStatistics::onEvent(const HWInstructionEvent &Event) {
   if (Event.Type == HWInstructionEvent::Retired)
     ++NumRetired;
 }