#253 code-completion cache per compiler set

[Oliver Stöneberg]

I got the main include files for my compiler in the
code-completion cache. The problem is, that the
code-completion cache is global and so all compiler
sets use the same completition-cache, what is quite
bad, if the include paths differ for the compiler sets.

Maybe there should be a compiler-based code-completion
cache, that is added the the global one.