Make sure -msign-return-address doesn't disable BTI support.

ok deraadt@

Author: kettenis

clang/lib/Driver/ToolChains/Clang.cpp

@@ -1588,7 +1588,10 @@ static void CollectARMPACBTIOptions(const ToolChain &TC, const ArgList &Args,
       D.Diag(diag::err_drv_unsupported_option_argument)
           << A->getSpelling() << Scope;
     Key = "a_key";
-    IndirectBranches = false;
+    if (Triple.isOSOpenBSD())
+      IndirectBranches = true;
+    else
+      IndirectBranches = false;
   } else {
     StringRef DiagMsg;
     llvm::ARM::ParsedBranchProtection PBP;