CMAKE_COMPILER_IS_GNU<LANG>
---------------------------

True if the compiler is GNU.

If the selected ``<LANG>`` compiler is the GNU compiler then this is ``TRUE``,
if not it is ``FALSE``.  Unlike the other per-language variables, this
uses the GNU syntax for identifying languages instead of the CMake
syntax.  Recognized values of the ``<LANG>`` suffix are:

::

  CC = C compiler
  CXX = C++ compiler
  G77 = Fortran compiler
