libc: Fix headers to allow direct inclusion.

These headers are missing a few #includes to allow their direct
inclusion from C

http://b.android.com/79841

Change-Id: Ifc712c17f4da70b26adb67d4d49ed659f53c3621

libc/include/android/dlext.h

@@ -18,7 +18,9 @@
 #define __ANDROID_DLEXT_H__
 
 #include <stddef.h>
+#include <stdint.h>
 #include <sys/cdefs.h>
+#include <sys/types.h>  /* for off64_t */
 
 __BEGIN_DECLS