Re-add dlmalloc for 32 bit.

It turns out that appportable has a version that calls dlmalloc directly.
Re-add the dlmalloc symbol for 32 bit only as a compatibility shim that
calls malloc.

Bug: 17881362
Change-Id: I8f20963b0b8d323489dc083e4063779e0d1d7447

libc/bionic/dlmalloc.h

@@ -34,11 +34,14 @@
 
 #define malloc_getpagesize getpagesize()
 
-/* dlmalloc_usable_size was exposed in the NDK, so change the name
- * of the function on 32 bit architectures.
- */
 #if !defined(__LP64__)
+/* dlmalloc_usable_size and dlmalloc were exposed in the NDK and some
+ * apps actually used them. Rename these functions out of the way
+ * for 32 bit architectures so that ndk_cruft.cpp can expose
+ * compatibility shims with these names.
+ */
 #define dlmalloc_usable_size dlmalloc_usable_size_real
+#define dlmalloc dlmalloc_real
 #endif
 
 /* Export two symbols used by the VM. */

libc/bionic/ndk_cruft.cpp

@@ -320,4 +320,10 @@ extern "C" size_t dlmalloc_usable_size(void* ptr) {
   return malloc_usable_size(ptr);
 }
 
+// Older versions of appportable used dlmalloc directly instead of malloc,
+// so export this compatibility shim that simply calls malloc.
+extern "C" void* dlmalloc(size_t size) {
+  return malloc(size);
+}
+
 #endif