Starting with Xcode 12 Beta 2, builds that used to work on Apple Silicon
now break due to `Hardware#oldest_cpu` returning `:nehalem` [1].
This commit is the first in a series of improvements to
`Hardware#oldest_cpu`. It resolves the Xcode 12 Beta 2 issue for now.
[1]: https://github.com/Homebrew/brew/issues/7857#issuecomment-655536261
We have strings containing hardcoded ".dylib" extensions in homebrew-core.
To be able to bring linuxbrew-core and homebrew-core closer together,
I am introducing a new generic attribute that can be used in formulae.
Companion to https://github.com/Homebrew/brew/pull/7698.
Provide better, `odeprecated` messaging for
`depends_on :macos => :mavericks` and otherwise just fix up the code
that relied on `:mavericks`.
There are formulae that use resource blocks for stuff that is needed in
test blocks. If a resource is a `.zip` archive, one needs `unzip`
utility in `PATH` to extract it, but its only available at build-time,
so one observes an error like that for example:
```
==> brew test psftools --verbose
Testing psftools
==> Downloading https://www.zone38.net/font/pc8x8.zip
Already downloaded: /github/home/.cache/Homebrew/downloads/ea5f6a485687368ff5bc99e4cc43a49b06e081baa51a97ee6ddcd8d1b82d7963--pc8x8.zip
==> Verifying ea5f6a485687368ff5bc99e4cc43a49b06e081baa51a97ee6ddcd8d1b82d7963--pc8x8.zip checksum
unzip -o /github/home/.cache/Homebrew/downloads/ea5f6a485687368ff5bc99e4cc43a49b06e081baa51a97ee6ddcd8d1b82d7963--pc8x8.zip -d /tmp/d20200304-21389-ui0wr0
Error: psftools: failed
undefined method `shelljoin' for nil:NilClass
```
Of course this issue affects Linux the most, because of higher
probability that the system lacks `unzip` for example.
With this commit, all resource guessed dependencies should be available
at build and test time.
We're not actually using this anywhere and it makes the code
more complicated.
Relatedly, this PR fixes the issue where
`uses_from_macos "python@2" => :build` was valid on macOS but not
on Linux.
