pkgconf: drop-in replacement for pkg-config

[cho-m]

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[carlocab]

I suggest retiring pkg-config already too. i.e. Let's delete it and add a formula rename for pkg-config -> pkgconf.

[cho-m]

I suggest retiring pkg-config already too. i.e. Let's delete it and add a formula rename for pkg-config -> pkgconf.

That's a bit complicated as audit doesn't like usage of old names / aliases.

Assuming audit is not changed, either need to:

• Do a giant syntax-only migration of all pkg-config usage to pkgconf.
• Make pkg-config into a transitional formula that just installs pkgconf and then do the migration at a more leisurely pace. At the end, can squash pkg-config formula to either be a rename/alias of pkgconf.

[carlocab]

We can just add a temporary exception for pkg-config and do the migration gradually.

[Bo98]

Am OK with this PR given pkgconf and pkg-config are already conflicting.

In terms of switching our uses to pkgconf, the requirements are:

• pkgconf cannot conflict with pkg-config
• brew install pkg-config must continue to work (I'd probably go as far as saying it should continue to do so without warnings, i.e. as an alias)

Merging via renames and merging via alias however works completely differently. One uses the migrator mechanism and one doesn't. So will need to carefully test it.

I expect anything we do here to be "special", which may indeed mean adjusting things in brew to allow depends_on "pkg-config" (potentially for a long time/forever as it would affect so many third-party formulae).