* Set MK_OPENMP to yes by default only on amd64, for now.
* Bump __FreeBSD_version to signal this addition.
* Ensure gcc's conflicting omp.h is not installed if MK_OPENMP is yes.
* Update OptionalObsoleteFiles.inc to cope with the conflicting omp.h.
* Regenerate src.conf(5) with new WITH/WITHOUT fragments.
Relnotes: yes
PR: 236062
MFC after: 1 month
X-MFC-With: r344779