Make cataclysm compile in clang.

1. clang didn't like `point look_debug(point point=point(-256,-256));`
2. CXX is now set with ?= so if you have CXX=clang++ set in your environment, it won't be overriden.
3. Even though $(LD) was used to compile the cataclysm executable, it was passed arguments that only gcc and not ld accepts. Thus changed it from $(LD) to $(CXX)