Ninja: Fortran_BUILDING_INTRINSIC_MODULES not implemented

!10158 (merged) / !5518 (merged) added the Fortran_BUILDING_IN(S)TRINSIC_MODULES feature only for the Makefile generator. Using the Ninja generator, the parser's cmFortranSourceInfo::Intrinsics list is not used within cmcmd_cmake_ninja_depends_fortran. According to the discussion at !5518 (comment 974231) this was intentional, but undocumented.

I would have liked to use CMake to build the builtin modules in LLVMFlang which will not be feasible when not working in Ninja.