Add explicit include of unistd.h for getopt(3) and related variables.

lib/util/regress/strtofoo/strtobool_test.c

@@ -25,6 +25,7 @@
 #else
 # include "compat/stdbool.h"
 #endif
+#include <unistd.h>
 
 #include "sudo_compat.h"
 #include "sudo_util.h"

lib/util/regress/strtofoo/strtoid_test.c

@@ -21,6 +21,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <errno.h>
+#include <unistd.h>
 
 #include "sudo_compat.h"
 #include "sudo_util.h"

lib/util/regress/strtofoo/strtomode_test.c

@@ -20,6 +20,7 @@
 
 #include <stdio.h>
 #include <stdlib.h>
+#include <unistd.h>
 
 #include "sudo_compat.h"
 #include "sudo_util.h"

lib/util/regress/strtofoo/strtonum_test.c

@@ -22,6 +22,7 @@
 #include <stdlib.h>
 #include <limits.h>
 #include <errno.h>
+#include <unistd.h>
 
 #include "sudo_compat.h"
 #include "sudo_util.h"