Bump default MAXTSIZ (kern.maxtsiz) from 128MB to 32GB. The old limit
prevents one from running eg clang built with debug; the new one is
arbitrary (equal to MAXDSIZ) and... well, should be quite future-proof.

Same fix might be applicable to other 64 bit architectures; I'll ask
their respective maintainers to make sure it won't break anything.

Reviewed by: kib
MFC after: 2 weeks
Sponsored by: DARPA, AFRL
Differential Revision: https://reviews.freebsd.org/D10758