The `cask` attribute doesn't make as much sense on Linux but can be
ignored there. The advantage of this change is that (like #4086) it
allows figuring out the relevant cask for a formulae requirement on a
Linux machine.
In the installation whose prefix is other than /usr/local,
osxfuse library and include path must explicitly be specified during build.
Although brew's pkg-config is configured to prepend appropriates paths,
the prepended paths (/usr/local) supercede the original HOMEBREW_PREFIX.
This behavior will cause the linker to select libraries outside brew's tree.
By adding /usr/local to HOMEBREW_LIBRARY_PATHS, superenv ensures that appears
only after the HOMEBREW_PREFIX, and thus fixes this problem.
HOMEBREW_INCLUDE_PATHS is also configured like keg-only Formulae.
Dependency is another similar, related class and it's super confusing
to have some Requirements that are named *Dependency.
ClosesHomebrew/homebrew#38891.
Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>
