Created attachment 194917 [details]
patch to enable all options on 10.x
After r473980, devel/llvm60 is ready for OpenMP on all FreeBSD versions, except for 10.x.
I tried the attached patch to remove the blocking line for 10.x, and 10.x seems to build functional OpenMP on both, amd64 and i386.
A commit references this bug:
Date: Thu Sep 20 02:47:24 UTC 2018
New revision: 480151
Update to LLVM 7.0.0 Release.
Update LICENSE to include additional licenses of sub-components.
Enable LLDB and OPENMP on 10. 
PR: 229570 
Submitted by: Rainer Hurling <firstname.lastname@example.org> 
Sponsored by: DARPA, AFRL
FreeBSD 10 is EoL and the offending line is gone after ports r483807.