Rename "master" branch to "main" for glibc 2.35 release.

[DJ Delorie]

"Carlos O'Donell" <carlos@redhat.com> writes:
> No alias would be provided for the master branch;

This would invalidate decades of online documentation in an instant, and
for that alone I oppose this part of your proposal.

It will also break existing git checkouts, even if you write very clear
documenation (you did, right? ;) about how to "fix" a checked out master
branch.