pkg/55720: py-numpy fails to build on evbarm-aarch64 because gcc9

[gson%gson.org@localhost (Andreas Gustafsson)]

>Number:         55720
>Category:       pkg
>Synopsis:       py-numpy fails to build on evbarm-aarch64 because gcc9
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    pkg-manager
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Mon Oct 12 06:45:00 +0000 2020
>Originator:     Andreas Gustafsson
>Release:        NetBSD-current, source date 2020.10.11.10.12.53
>Organization:
>Environment:
Architecture: aarch64
Machine: evbarm
>Description:

>How-To-Repeat:

Running NetBSD-current on evbarm-aarch64, building the py-numpy package
from pkgsrc-current fails as follows:

  => Returning to build of py37-numpy-1.19.2
  => Full dependency gcc9>=9.0: NOT found
  => Verifying reinstall for ../../lang/gcc9
  => Bootstrap dependency digest>=20010302: found digest-20190127
  ERROR: This package is not available for these platforms: NetBSD-*-aarch64.
  ERROR: This package has set PKG_SKIP_REASON:
  ERROR: gcc9-9.3.0nb4 is not available for NetBSD-9.99.73-aarch64

This is with all default settings - the OS is freshly installed and
/etc/mk.conf is empty except for MAKE_JOBS.

>Fix: