I'd like to refer to this bug which seems to be still open and still present in all versions of LLVM since LLVM 4.0 (my guess, I did not track that down exactly).
Since this severe problem has not been solved even for LLVM 7.0, the issue not being able to use an ICD for multiple platforms available on FreeBSD in cases the OpenCL backends (lang/pocl (See https://github.com/pocl/pocl/issues/474), devel/beignet, lang/clover) are all compiled dynamically against the same LLVM backend. The issue disapperas were the backend is compiled against a different version of LLVM or statically linked. Both is inacceptable.
I'd like to refer to this LLVM bug:
Bug 30587 - Inconsistency in commandline options with multiple OpenCL vendor libraries installed :
*** This bug has been marked as a duplicate of bug 233495 ***