pa_mac_core: fix whitespace and missing semicolon

It compiled without the semicolon because it was followed by a VDBUG,
which was followed by a semicolon. The VDBUG was disabled so its
semicolon finished the line above.

test/patest_write_stop_hang_illegal.c

@@ -43,6 +43,7 @@
  */
 
 #include <stdio.h>
+#include <unistd.h>
 #include <math.h>
 #include <memory.h>
 /* pthread may only be available on Mac and Linux. */