Otherwise it's possible that certain buildtime dependencies, that won't
be linked against, will block a build.

See Homebrew/homebrew#23115.

Copy these files/folders to a .bottle directory under the Cellar for installation
elsewhere at pouring time.

Temporarily disable HOMEBREW_GIT_ETC methods until fixed.

This method allows copying a file to a new location by performing a
substitution on the pathname.

If an etc file exists on installation instead of overwriting it (or
requiring all the manual checks in formula) simply copy it with the
extension `.default` appended.

Fixes Homebrew/homebrew#23115.

This reverts commit 5e26584736b310c365d4b9cce99d0dced9a2d309.