Bump __FreeBSD_version for the following (weak) reasons:
o Sources that are shared between kernel and userland and that may

contain references to DDB or any of its functions may need to
know this.

o Userland tools may include <machine/gdb_machdep.h> from now on.

Think kernel debugger...

o The kernel core file now contains the TID of the kernel thread

that made the dump.