Driver: Allow build system override of default non-fragile ABI version.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@118786 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Driver/Tools.cpp b/lib/Driver/Tools.cpp
index bf40760..eb5c8ab 100644
--- a/lib/Driver/Tools.cpp
+++ b/lib/Driver/Tools.cpp
@@ -1425,7 +1425,11 @@
                        options::OPT_fno_objc_nonfragile_abi,
                        getToolChain().IsObjCNonFragileABIDefault())) {
         // Determine the non-fragile ABI version to use.
+#ifdef DISABLE_DEFAULT_NONFRAGILEABI_TWO
+        unsigned NonFragileABIVersion = 1;
+#else
         unsigned NonFragileABIVersion = 2;
+#endif
 
         if (Arg *A = Args.getLastArg(
               options::OPT_fobjc_nonfragile_abi_version_EQ)) {