When we switch powerpc64 to clang/elfv2 by default, several ports will break due to the -mminimal-toc flag being no longer accepted.
This preliminary patch conditionalizes the setting of the flag.
As of yet, the switch it uncommitted. So, a dummy OSVERSION is used. This will allow the existing tree to be regression-tested before the switch. Interested testers should set the bogus OSVERSION to a real value.