build fixes

[dhewg]

This fixes 2 build error I ran into:

• u-boot builds a python module, which currently requires installed python2 headers
  backport python3 patches and add a dependency for Python3:host, so it works everywhere
• libgpg-error wrt gawk and variable names of reserved keywords

[InuSasha]

i think this is superseeded by toolchain.
because Python3:host is part of the toolchain. (toolchain > toolchain:host > meson:host > Python3:host)

[InuSasha]

Thanks for your contribution.

Are the u-boot patches from upstream?
ok, i had to read commit messages, first. patches are from upstream

[MilhouseVH]

@dhewg did you see #3965 which also includes a fix for u-boot?

[dhewg]

@MilhouseVH nope, and that's certainly smaller, I wasn't sure if non-release versions are acceptable ;)
So I guess I'll rebase this with just the gpg error?

[chewitt]

Looking at u-boot patchwork it's clear they are still finding issues with Python 3, so check which patches overlap (or not) .. don't assume someone else found them all.

[MilhouseVH]

@dhewg the PR I referenced may be open for a short while (will certainly merge no later than the death of Python2) to allow for testing and during that time we can continue to bump u-boot (bringing in any remaining Python3 fixes) and eventually bumping to a release version. But yes, best to drop the u-boot changes in this PR and use the #3965 instead.

Dev snapshots are acceptable in master if there's a good reason (and avoiding multiple patches is one such reason) but tagged versions are preferred when available.

For the libgpg-error issue this is the upstream fix: gpg/libgpg-error@7865041 - I would suggest adding this patch in preference to the sed workaround.

[dhewg]

Done, but I had to add an extra hunk for Makefile.in because of autocrap