Log Message:
lang/rust: Mark BROKEN_ON_PLATFORM for NetBSD-7*-i386

As discussed on pkgsrc-users, mark rust as BROKEN_ON for NetBSD 7
i386.  The bootstrap is built for 8, apparently because it doens't
build on 7.  This is BROKEN_ON not NOT_FOR because it does make sense
to want rust on 7 -- it just won't build.

(Probably this should be expanded to all arches and all versions < 8.)