cl/gcc-adapt-ext: <cp/cp-tree.h> moved to correct position.

NOTE: Related to issue #2 ->> fixing the compilation for newer versions
      of gcc. Also, conditional compilation added.
cl/gcc-adapt-ext: Added conditional compilation for <cp/cp-tree.h>.

NOTE: Related to issue #2 ->> This header file's position is dependent
      on the version of the GCC used, at is seems.