[asan] fix Android build (mark asan_malloc_usable_size as an interface function)

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@183651 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/asan/asan_allocator2.cc b/lib/asan/asan_allocator2.cc
index b1fb684..4b1b643 100644
--- a/lib/asan/asan_allocator2.cc
+++ b/lib/asan/asan_allocator2.cc
@@ -674,6 +674,7 @@
   return 0;
 }
 
+SANITIZER_INTERFACE_ATTRIBUTE
 uptr asan_malloc_usable_size(void *ptr, StackTrace *stack) {
   CHECK(stack);
   if (ptr == 0) return 0;