- cache warning output messages?
- compressed files in the cachedirectory ??
- gcc -g3 places #define __TIME__ "17:23:52" into the preprocessor
  output which means that each time there will be a recompilation
  and never a cache hit. so this must be removed from preprocessor
  output ??? yes but only remove the __TIME__ #define and nothing else
  and leave a #define __TIME__ compilercache_unfied there...
  and only do this in debug mode...
- -Wp erase? sure that this is allowed? problem autoconf does -Wp
  but make dist creates archive that won't do -Wp
  so cache won't hit.
