For some reason check_cxx_compiler_flag() passes result variable name down to
compiler:
https://github.com/Kitware/CMake/blob/master/Modules/CheckCXXSourceCompiles.cmake#L57

But compiler doesn't permit dashes in macro name, like in
-DHAVE_CXX_-fimplicit-templates.

Workarounded by renaming HAVE_CXX_-fimplicit-templates to
HAVE_CXX_IMPLICIT_TEMPLAES.