Fix <sys/endian.h> uint32_t build failures.

Change-Id: I833b51318f0bf7749073859b7ffacc668c27558e
diff --git a/libc/include/sys/endian.h b/libc/include/sys/endian.h
index 1186540..be4c905 100644
--- a/libc/include/sys/endian.h
+++ b/libc/include/sys/endian.h
@@ -39,6 +39,8 @@
 #include <sys/cdefs.h>
 #include <machine/endian.h>
 
+#include <stdint.h>
+
 #define _LITTLE_ENDIAN	1234
 #define _BIG_ENDIAN	4321
 #define _PDP_ENDIAN	3412