Added include of cstdlib needed for strtol, strtod and getenv.

src/commandlineflags.cc

@@ -17,6 +17,7 @@
 #include <cstring>
 #include <iostream>
 #include <limits>
+#include <cstdlib>
 
 namespace benchmark {
 // Parses 'str' for a 32-bit signed integer.  If successful, writes