There is now an option [Homebrew]/Enabled that can be used to toggle use
of homebrew packages on MacOS. It defaults to true if the brew command is
found and false if it isn't. If enabled we add the gettext, libarchive and
email@example.com library and include directories to
CMAKE_LIBRARY_PATH/CMAKE_INCLUDE_PATH/PKG_CONFIG_PATH so that cmake finds
the libraries. It also prepends the bison/bin directory to $PATH since the
system one is too old.
It also introduces an experimental option [Hombrew]/qt which can be set in
order to use Qt5 from homebrew. If it is set to "disabled" (default) the
current behaviour is kept. Otherwise it can be set to a given version (such
as 5.10.0) so that $(brew --cellar qt)/5.10.0/bin is used to find qmake.
It can also be set to "latest" to use whatever is the latest version that
has been installed by homebrew.