To allow
depends_on :x11 => :optional
and friends to work as expected, make requirements record any tags and
add special handling to the X11Dependency to record both a minimum
version and additional tags.
Signed-off-by: Jack Nagel <jacknagel@gmail.com>
ComparableSet only allows a single object of a given class,
choosing the object with the greatest value. This was mainly created
for Requirements, so that, e.g., two X11Dependencies of differing
strictness don't both end up in the same requirement set.
FixesHomebrew/homebrew#15240.