Hide __libc_malloc_dispatch.

Now that -Bsymbolic is fixed, we can hide __libc_malloc_dispatch without
breaking ASAN.

Bug: 11156955
Change-Id: Ia2fc9b046a74e666b33aa6c6c5435f70a63b8021

libc/bionic/malloc_debug_common.cpp

@@ -81,8 +81,7 @@ static const MallocDebug __libc_malloc_default_dispatch __attribute__((aligned(3
 };
 
 // Selector of dispatch table to use for dispatching malloc calls.
-// TODO: fix http://b/15432753 and make this static again.
-const MallocDebug* __libc_malloc_dispatch = &__libc_malloc_default_dispatch;
+static const MallocDebug* __libc_malloc_dispatch = &__libc_malloc_default_dispatch;
 
 // Handle to shared library where actual memory allocation is implemented.
 // This library is loaded and memory allocation calls are redirected there