Bootstrap crunchgen after removing -dc from linker invocation

In ec81497cc726 crunchgen was updated to remove -dc from the linker
invocations in its generated makefile output, as this flag is no longer
necessary, and is going to be an error with lld 15.

Update the BOOTSTRAPPING conditions for copying the crunchgen binary
from the host, or actually bootstrapping it when necessary. Since
ec81497cc726 did not bump __FreeBSD_version, I have chosen the nearest
values.

Fixes: ec81497cc726
MFC after: 3 days