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/development/libraries/podofo/default.nix

@@ -11,12 +11,12 @@ stdenv.mkDerivation rec {
 
   propagatedBuildInputs = [ zlib freetype libjpeg libtiff fontconfig openssl libpng ];
   nativeBuildInputs = [ cmake ];
-  buildInputs = [ lua5 stdenv.gcc.libc ];
+  buildInputs = [ lua5 stdenv.cc.libc ];
 
   crossAttrs = {
     propagatedBuildInputs = [ zlib.crossDrv freetype.crossDrv libjpeg.crossDrv
       libtiff.crossDrv fontconfig.crossDrv openssl.crossDrv libpng.crossDrv
-      lua5.crossDrv stdenv.gccCross.libc ];
+      lua5.crossDrv stdenv.ccCross.libc ];
   };
 
   # fix finding freetype-2.5