unifdef: update to 2.12, adopt

[wbp11]

Testing the changes

• I tested the changes in this PR: YES

Local build testing

• I built this PR locally for my native architecture: x86_64-glibc
• I built this PR locally for these architectures (if supported. mark crossbuilds):
  • x86_64-musl (masterdir)
  • i686 (masterdir)
  • aarch64 (cross)
  • aarch64-musl (cross)
  • armv6l (cross)
  • armv6l-musl (cross)
  • armv7l (cross)
  • armv7l-musl (cross)

[wbp11]

There was no issue fetching the source right before I opened the PR. I just tried it again and it worked fine.