gcc_multi: prevent overwritten libs after 51f1b4ec48d

pkgs/development/compilers/gcc/4.8/default.nix

···
 
 # Strip kills static libs of other archs (hence cross != null)
 // optionalAttrs (!stripped || cross != null) { dontStrip = true; NIX_STRIP_DEBUG = 0; }
+
+// optionalAttrs (enableMultilib) { dontMoveLib64 = true; }
 )