Make the _Unwind_Ptr declaration match clang's.

Bug: https://issuetracker.google.com/37126620
Test: builds, boots angler
Change-Id: I7d4a9b998f2e5c4c7b0beed87807d7b76a564c5c
diff --git a/libc/include/link.h b/libc/include/link.h
index 0d07cb9..dd3b99f 100644
--- a/libc/include/link.h
+++ b/libc/include/link.h
@@ -28,6 +28,7 @@
 #ifndef _LINK_H_
 #define _LINK_H_
 
+#include <stdint.h>
 #include <sys/cdefs.h>
 #include <sys/types.h>
 
@@ -55,7 +56,7 @@
 #endif
 
 #ifdef __arm__
-typedef long unsigned int* _Unwind_Ptr;
+typedef uintptr_t _Unwind_Ptr;
 _Unwind_Ptr dl_unwind_find_exidx(_Unwind_Ptr, int*);
 #endif