make asan work at -O0, clang part. Patch by glider@google.com

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@145531 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/BackendUtil.cpp b/lib/CodeGen/BackendUtil.cpp
index 048011d..c182790 100644
--- a/lib/CodeGen/BackendUtil.cpp
+++ b/lib/CodeGen/BackendUtil.cpp
@@ -150,6 +150,8 @@
   if (LangOpts.AddressSanitizer) {
     PMBuilder.addExtension(PassManagerBuilder::EP_ScalarOptimizerLate,
                            addAddressSanitizerPass);
+    PMBuilder.addExtension(PassManagerBuilder::EP_EnabledOnOptLevel0,
+                           addAddressSanitizerPass);
   }
   
   // Figure out TargetLibraryInfo.