fix remaining trace of GCC_VERSION
fix shared library linker flags on linux
handle version 4.x.y numbers
and made to work on generic clang instances

Tested on Debian Wheezie
Merge branch 'F-FixOnDebian'

* F-FixOnDebian:
  work on generic clang instances
  handle version 4.x.y numbers
  fix shared library linker flags on linux
  fix remaining trace of GCC_VERSION