Change occurrences of gcc to the more general cc

This is done for the sake of Yosemite, which does not have gcc, and yet
this change is also compatible with Linux.

pkgs/stdenv/adapters.nix

@@ -8,7 +8,7 @@ rec {
 
 
   # Override the compiler in stdenv for specific packages.
-  overrideGCC = stdenv: gcc: stdenv.override { allowedRequisites = null; inherit gcc; };
+  overrideGCC = stdenv: gcc: stdenv.override { allowedRequisites = null; cc = gcc; };
 
 
   # Add some arbitrary packages to buildInputs for specific packages.
@@ -235,9 +235,4 @@ rec {
       });
     };
 
-  dropCxx = drv: drv.override {
-    stdenv = if pkgs.stdenv.isDarwin
-      then pkgs.allStdenvs.stdenvDarwinNaked
-      else pkgs.stdenv;
-  };
 }