Bug 981558: Test _MSC_VER instead of _WIN32 for the code that uses

the __int64 type because gcc on Windows doesn't support the i64
integer literal suffix and the use of I64 in printf format specifiers.
TBR=gk.

config/now.c

@@ -19,7 +19,7 @@ int main(int argc, char **argv)
      * of this program and omit the library build time
      * in PRVersionDescription.
      */
-#elif defined(_WIN32)
+#elif defined(_MSC_VER)
     __int64 now;
     time_t sec;