(Only the first 10 of 17 ports in this commit are shown above. )
OPTIONS_SET/OPTIONS_UNSET are global variables, they cannot be used in ports
Makefiles.
So, replace them with OPTIONS_SLAVE, OPTIONS_EXCLUDE, OPTIONS_DEFAULT,
where appropriate.
The ghostscript ports are doing something nasty that is certainly wrong,
but I don't want to try to understand it.
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