gfortran: 10 for netbsd-10, and getting a full dependency on gfortran in a meta package

[Greg Troxel <gdt%lexort.com@localhost>]

I have a meta package for home assistant dependencies in wip.  It's not
really possible to package it, because it has lots of exact python
dependencies.  So the package is just to depend on what is needed to
install it in a venv; that's as good as it gets.

1) Some of the python things that get installed in the venv need
fortran, so I want a full dependency on the fortran compiler.  Currently
it just depends on gcc7, which is ok on netbsd-9, but on NetBSD 10 there
is gcc10 and it seems we should use gcc10 for gfortran.  However, with
META_PACKAGE, USE_LANGUAGES is ignored, and hence _USE_GFORTRAN is
turned off.  I don't see any I_WANT_A_FULL_DEP_ON_A_FORTRAN_COMPILER
knob.

What do people think the right way is to express

  choose the fortran compiler that pkgsrc would use

  depend on it fuly

?

2) On NetBSD 10 (not arm), gfortran.mk chooses gcc7.  I added

  +# On NetBSD 10, default to gcc 10 to match base, instead of 7.                                                                                     
  +.if ${OPSYS} == "NetBSD" && empty(OS_VERSION:M[0-9].*)                                                                                             
  +POSSIBLE_GFORTRAN_VERSION=     10                                                                                                                  
  +.endif                                                                                                                                             

and then it defaults to 10.  Any objections to committing?   It's a
little close to freeze, but it seems broken to drag in an old version.

Other approaches?