[llvm-dev] Tag for using git describe on master

[Hans Wennborg via llvm-dev]

As first discussed in the giant "New LLVM git repository conversion
prototype" thread, I've pushed a git tag that allows git-describe to
be used for generating human readable commit names on master.

The tag is "llvmorg-10-init", to be interpreted as "the initial commit
with major version number 10". The idea is to add similar tags along
with future version bumps.

git describe generates a name like this:

$ git describe a4783ef
llvmorg-10-init-8348-ga4783ef58d3

Where "llvmorg-10-init" is the tag name, 8348 is the number of commits
since the tag (yay, monotonically incrementing commit numbers), and
"a4783ef58d3" is the hash with "g" as a magic prefix to indicate it's
a git hash.

The name can be used to refer to commits directly (git only looks at
the hash after the "g"):

$ git show llvmorg-10-init-8348-ga4783ef58d3 -s --oneline
a4783ef58d3 [Alignment][NFC] getMemoryOpCost uses MaybeAlign


Thanks,
Hans