Use stack protector strong by default on OpenBSD.

Use stack protector strong by default to match the base OS and ports/packages
compiler policy.

Patch by Brad Smith.

llvm-svn: 209432
diff --git a/clang/lib/Driver/ToolChains.h b/clang/lib/Driver/ToolChains.h
index 7d69f7b..13e9d67 100644
--- a/clang/lib/Driver/ToolChains.h
+++ b/clang/lib/Driver/ToolChains.h
@@ -534,7 +534,7 @@
   bool isPIEDefault() const override { return true; }
 
   unsigned GetDefaultStackProtectorLevel(bool KernelOrKext) const override {
-    return 1;
+    return 2;
   }
 
 protected: