Build system related fixes

While trying to package godot for fedora I encountered some issues and fixed them right away. 

The first patch addresses the CCFLAGS handling which was broken, CFLAGS, since not touched anywhere else works as expected though.

The second patch is a bit bigger, in order to support building godot without all the bundled libraries, which is necessary for packages which are introduced to the packaging system of any distribution I know, I had to make the bundled libraries optional. 
Now by specifying dynlink=yes you can leverage the libraries installed on the system. Of course this is not perfect, however now the bundled libraries are becoming optional :+1: