cl/gcc-adapt-ext: GCC_PLUGIN_VERSION is used instead of GCC_HOST_4_9...

NOTE: GCC_PLUGIN_VERSION is a number for representing the version of GCC
      used. For older versions of GCC this macro is set to 0.

      Resolves the #3 issue @ <https://github.com/deekej/predator/>.
Merge branch 'extension/gcc-version-macro-obtaining' into cl/gcc-adapt-ext