Remove GNU-specific <getopt.h>. getopt() is defined in <unistd.h> in POSIX, which adding #define _XOPEN_SOURCE 500 causes GCC to include.

src/asm/main.c

@@ -5,8 +5,8 @@
  *
  */
 
+#define _XOPEN_SOURCE 500
 #include <math.h>
-#include <getopt.h>
 #include <stdarg.h>
 #include <stdbool.h>
 #include <stdio.h>

src/fix/main.c

@@ -14,7 +14,7 @@
  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  */
 
-#include <getopt.h>
+#define _XOPEN_SOURCE 500
 #include <stdbool.h>
 #include <stdint.h>
 #include <stdio.h>

src/link/main.c

@@ -1,4 +1,4 @@
-#include <getopt.h>
+#define _XOPEN_SOURCE 500
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>