getopt: Fix macro redefinition warning

We already define _CRT_SECURE_NO_WARNINGS

externals/getopt/getopt.c

@@ -35,7 +35,6 @@ PROFITS, BUSINESS INTERRUPTION, LOSS OF PROGRAMS OR OTHER DATA ON
 YOUR INFORMATION HANDLING SYSTEM OR OTHERWISE, EVEN If WE ARE
 EXPRESSLY ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.
 */
-#define _CRT_SECURE_NO_WARNINGS
 #include <stdlib.h>
 #include <stdio.h>
 #ifdef _MSC_VER