stdenv: fix evaluation if !stdenv.cc.hasCC

stdenv.cc may throw, e.g. in the case of pkgsCross.ghcjs where we must
not force it for the purpose of attribute accessing (`or` doesn't
implicitly tryEval…).

Regression introduced in 1a5bd697ad.

pkgs/stdenv/generic/make-derivation.nix

@@ -250,9 +250,10 @@ let
     "stackprotector"
     "strictoverflow"
   ];
-  defaultHardeningFlags = stdenv.cc.defaultHardeningFlags or
-    # fallback safe-ish set of flags
-    (remove "pie" knownHardeningFlags);
+  defaultHardeningFlags =
+    (if stdenv.hasCC then stdenv.cc else {}).defaultHardeningFlags or
+      # fallback safe-ish set of flags
+      (remove "pie" knownHardeningFlags);
   enabledHardeningOptions =
     if builtins.elem "all" hardeningDisable'
     then []