utils/git: Add linkify script.

[pcc]

This script linkifies (i.e. makes clickable in the terminal) text that appears
to be a pull request or issue reference (e.g. #12345 or PR12345) or a
40-character commit hash (e.g. abc123). You can configure git to automatically
send the output of commands that pipe their output through a pager, such as
git log and git show, through this script by running this command from
within your LLVM checkout:

git config core.pager 'llvm/utils/git/linkify | pager'

The pager command is run from the root of the repository even if the git
command is run from a subdirectory, so the relative path should always work.

It requires OSC 8 support in the terminal. For a list of compatible terminals,
see https://github.com/Alhadis/OSC8-Adoption

[MaskRay]

Thanks! This is useful.

[MacDue]

For this to work for me I have to do:

# Note: pager is an alias of less (here)
git config core.pager 'llvm/utils/git/linkify | pager -r'

-r forces less to interpret the ANSI codes.

Otherwise, it appears as:

 (8;;https://github.com/llvm/llvm-project/issues/101748#1017488;;)

---

Also, there may be some security implications from that... but I assume you can treat the LLVM repo as safe.

[pcc]

Interesting. For me I have LESS=FRX in the pager environment. This is added by Git when it launches the pager; the R causes it to interpret ANSI codes. Maybe you are overriding LESS to something else? Do you have colors enabled (git config color.ui) and do they display properly?