Make the _Unwind_Ptr declaration match clang's.

Bug: https://issuetracker.google.com/37126620
Test: builds, boots angler
Change-Id: I7d4a9b998f2e5c4c7b0beed87807d7b76a564c5c
diff --git a/linker/linker.cpp b/linker/linker.cpp
index f43d6fc..39062e6 100644
--- a/linker/linker.cpp
+++ b/linker/linker.cpp
@@ -361,16 +361,14 @@
 //
 // Intended to be called by libc's __gnu_Unwind_Find_exidx().
 _Unwind_Ptr do_dl_unwind_find_exidx(_Unwind_Ptr pc, int* pcount) {
-  uintptr_t addr = reinterpret_cast<uintptr_t>(pc);
-
   for (soinfo* si = solist_get_head(); si != 0; si = si->next) {
-    if ((addr >= si->base) && (addr < (si->base + si->size))) {
+    if ((pc >= si->base) && (pc < (si->base + si->size))) {
         *pcount = si->ARM_exidx_count;
         return reinterpret_cast<_Unwind_Ptr>(si->ARM_exidx);
     }
   }
   *pcount = 0;
-  return nullptr;
+  return 0;
 }
 
 #endif