wrong cmake tab completion for CMAKE_COMPILER_IS_GNUCC

message("IS_GNUC: ${CMAKE_COMPILER_IS_GNUC} IS_GNUCC: ${CMAKE_COMPILER_IS_GNUCC}")

% cmake .
IS_GNUC:  IS_GNUCC: 1

% grep -roh 'CMAKE_COMPILER_IS_GNU[^) ]\+' \
    c:/Program\ Files/CMake/share/cmake-3.6/ | sort | uniq -c
      1 CMAKE_COMPILER_IS_GNU<LANG>
      1 CMAKE_COMPILER_IS_GNUC
     14 CMAKE_COMPILER_IS_GNUCC
      1 CMAKE_COMPILER_IS_GNUCC@
      2 CMAKE_COMPILER_IS_GNUCC}"
     21 CMAKE_COMPILER_IS_GNUCXX
      1 CMAKE_COMPILER_IS_GNUCXX@
      2 CMAKE_COMPILER_IS_GNUCXX}"
      5 CMAKE_COMPILER_IS_GNUG77
      1 CMAKE_COMPILER_IS_GNUG77@
      1 CMAKE_COMPILER_IS_GNULANG