I see the new OpenMP library is now committed. Unfortunately some ports will automatically pick up any OpenMP libraries without express permission of the porter. Or any inclusion in WANTLIB or LIB_DEPENDS.
Examples include math/z3, audio/libsoxr, graphics/libraw. I explored a bunch of these years ago and some were patched to force OpenMP off. Some were not, and of course in the meanwhile some can change. In general I believe OpenMP should be turned off (the Makefile adjusted to disable any OpenMP library.) It should be up to porters to choose and of course to document how to control the number of threads in a port-specific way. Most ports will compute OMP_NUM_THREADS=<cpu count> which is rarely what you want. Ports like math/armadillo and math/eigen3 are source-only ports (or mostly) and the user/programmer selects OpenMP directly, so no change is needed for these. J
