Fix sysconf return type

Summary: The sysconf return type is supposed to be long, not unsigned.

Reviewed By: Orvid

Differential Revision: D4350903

fbshipit-source-id: 29d86081bf75d123e76b831a669b0fd3936ce102

folly/detail/CacheLocality.cpp

@@ -43,7 +43,7 @@ static CacheLocality getSystemLocalityInfo() {
   }
 #endif
 
-  size_t numCpus = sysconf(_SC_NPROCESSORS_CONF);
+  long numCpus = sysconf(_SC_NPROCESSORS_CONF);
   if (numCpus <= 0) {
     // This shouldn't happen, but if it does we should try to keep
     // going.  We are probably not going to be able to parse /sys on