[llvm-mca] Use an ordered map to collect hardware statistics. NFC.

Histogram entries are now ordered by key.  This should improves their
readability when statistics are printed.

llvm-svn: 334961
diff --git a/llvm/tools/llvm-mca/DispatchStatistics.h b/llvm/tools/llvm-mca/DispatchStatistics.h
index 3b735a1..7b98a84 100644
--- a/llvm/tools/llvm-mca/DispatchStatistics.h
+++ b/llvm/tools/llvm-mca/DispatchStatistics.h
@@ -35,9 +35,9 @@
 #define LLVM_TOOLS_LLVM_MCA_DISPATCHVIEW_H
 
 #include "View.h"
-#include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/MC/MCSubtargetInfo.h"
+#include <map>
 
 namespace mca {
 
@@ -49,7 +49,7 @@
   // is one counter for every generic stall kind (see class HWStallEvent).
   llvm::SmallVector<unsigned, 8> HWStalls;
 
-  using Histogram = llvm::DenseMap<unsigned, unsigned>;
+  using Histogram = std::map<unsigned, unsigned>;
   Histogram DispatchGroupSizePerCycle;
 
   void updateHistograms() {