Fix mac sdk build.

Add include files for types and functions that were not included properly.

Change-Id: I4849f5bdf535c6eec9254228cf980c30d11a5a1b
diff --git a/libcutils/threads.c b/libcutils/threads.c
index 9400441..5f5577b 100644
--- a/libcutils/threads.c
+++ b/libcutils/threads.c
@@ -21,6 +21,8 @@
 // For gettid.
 #if defined(__APPLE__)
 #include "AvailabilityMacros.h"  // For MAC_OS_X_VERSION_MAX_ALLOWED
+#include <stdint.h>
+#include <stdlib.h>
 #include <sys/syscall.h>
 #include <sys/time.h>
 #include <unistd.h>