More debug malloc fixes.

Include the leaky executable's name in the log output. Fix the "sh" test.
Use uintptr_t instead of intptr_t.

Also fix debug formatting of NULL with %s.

Bug: 7291287
Change-Id: I015bf341cd48d43a247173612e6ccb1bf1243d53
diff --git a/libc/bionic/malloc_debug_common.h b/libc/bionic/malloc_debug_common.h
index 3d12f87..e15ccd0 100644
--- a/libc/bionic/malloc_debug_common.h
+++ b/libc/bionic/malloc_debug_common.h
@@ -57,7 +57,7 @@
     // fields above "size" are NOT sent to the host
     size_t size;
     size_t allocations;
-    intptr_t backtrace[0];
+    uintptr_t backtrace[0];
 };
 
 struct HashTable {