USE_LINUX assumes anything built by a linux toolchain targets linuxulator. In some cases a port may want to build either for native (e.g. using proprietary toolchain) or for unsupported ABI (e.g. FreeBSD<->device bridge).
To fix maybe extend the syntax to allow arguments (similar to USES) e.g.,
to avoid hacks like in devel/fb-adb:
Am I allowed to add a +1 here?
If so, consider this my vote to add this feature.
(In reply to Chris Hutchinson from comment #1)
Don't ask for permission when it comes to communication :) Feedback is important, and we don't have the 'vote' feature turned on. Ideally, the feedback is more than just a "+1", but also explains/confirms/reiterates the value/benefit to you :)
CC'ing tijl as he works on USES=linux and may (or not) want to tackle :build argument similar to USES=python:build.
Can you check that the changes made to devel/fb-adb in bug 211645 are correct?
Fixed in ports r421387.