[ASan] make sure __asan_default_options symbol is exported

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@161873 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/asan/asan_rtl.cc b/lib/asan/asan_rtl.cc
index a798314..f1b4e62 100644
--- a/lib/asan/asan_rtl.cc
+++ b/lib/asan/asan_rtl.cc
@@ -244,6 +244,7 @@
     case 28: __asan_stack_free(0, 0, 0); break;
     case 29: __asan_stack_malloc(0, 0); break;
     case 30: __asan_set_on_error_callback(0); break;
+    case 31: __asan_default_options(); break;
   }
 }