include lib/i18n_module in user sources

It's used by the libc build to determine the citrus module version,
so including it will give us consistent results both with a full
NetBSD checkout and a rumprun things only checkout.
Add two more Makefile conditionals required for RUMPRUN=yes

 * do not build _errno.c (different thread/tls handling)
 * do not build either phk- or jemalloc (different backing page allocation)

Somehow I missed these in the previous commit, but now libc built with
RUMPRUN=yes works also with rumprun-posix, so there's reasonably high
confidence that I didn't miss anything anymore.
Change a KASSERT to KASSERTMSG and print enough details about the callout
so it can be identified even if ddb should not be helpfull (or not enabled).
Use correct pinset function (5 not 2) for gmac on BananaPi