Free PressureDiffs instead of leaking.

Found by valgrind.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@189725 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/RegisterPressure.h

@@ -157,6 +157,7 @@ class PressureDiffs {
   unsigned Max;
 public:
   PressureDiffs(): PDiffArray(0), Size(0), Max(0) {}
+  ~PressureDiffs() { free(PDiffArray); }
 
   void init(unsigned N);