Change Benchmark UserCounter to 64 bit int

Summary: Change UserCounters to 64bit integer to fit big counters like cpu_cycle counting.

Reviewed By: yfeldblum

Differential Revision: D18249661

fbshipit-source-id: 7808ef51e7230aa929ed555ed837ba5dd1962944

folly/Benchmark.cpp

@@ -337,7 +337,7 @@ class BenchmarkResultsPrinter {
               break;
             case UserMetric::Type::CUSTOM:
             default:
-              printf("  %-*d", int(name.length()), ptr->value);
+              printf("  %-*" PRId64, int(name.length()), ptr->value);
           }
         } else {
           printf("  %-*s", int(name.length()), "NaN");

folly/Benchmark.h

@@ -57,11 +57,11 @@ class UserMetric {
  public:
   enum class Type { CUSTOM, TIME, METRIC };
 
-  int value{};
+  int64_t value{};
   Type type{Type::CUSTOM};
 
   UserMetric() = default;
-  /* implicit */ UserMetric(int val, Type typ = Type::CUSTOM)
+  /* implicit */ UserMetric(int64_t val, Type typ = Type::CUSTOM)
       : value(val), type(typ) {}
 };