This is not numpy's problem. I also commented in the PR but it bears repeating, anything built with GCC, including with gfortran in this case, needs the GCC libraries to operate properly. flang exists but I haven't had a chance to try building with it yet, but is part of the larger overhaul.
If you're toggling non-default options on a port like numpy, you really need to understand the consequences of it.
In the Python world, we cannot underestimate pilot errors. You need to consider the userbase of numpy, many of whom are not necessarily as versed in software like we are, and just see "ooh reduce dependency". Disabling fortran support is a pretty fatal one.
As for the proposed changes themselves, these will not apply after numpy is switched to building under PEP-517, amongst other things.
Can you suggest a better approach that would be compatible going forawrd? (When is the PEP-517 switch actually going to happen?)
It's been in my tree for quite some time, but simply missing some sanity checks.
It's unfortunate that we couldn't have gotten python@ feedback of this sort on this at any point in the last three years that the PR has been open- I guess we need more python@ staffing. =\
It's also unfortunate that the Python ecosystem overall has a very particular way of doing things and is a mess to even start learning.