Disabling CMAKE_OSX_ARCHITECTURES on CMake

[Mojca Miklavec]

Hi,

The following ticket:
   https://trac.macports.org/ticket/37732
"cmake portgroup needs an option to disable use of CMAKE_OSX_ARCHITECTURES"

is something that requires a trivial change, but without the patch
several ports using Fortran and CMake have serious problems (OK, CMake
on Root was still broken when I last tried and PLplot has serious
problems with the CMake setup, but nevertheless - it's a bit painful).

In the meantime I think I could fix the issue myself, but I'm not sure
what the strategy should be, for example:

(a) never add CMAKE_OSX_ARCHITECTURES if not building universal and if
native platform equals the target one

(b) never add CMAKE_OSX_ARCHITECTURES if Fortran is involved (then the
port needs an explicit flag to tell CMake/MacPorts that it's using
fortran)

(c) a special flag like "cmake.use_osx_architectures no"

Can someone please take a look into this?

Thank you,
    Mojca