Just found that GNU configure gets passed a crippled --host
and tracked it down to MACHINE_GNU_ARCH not properly set
in pkgsrc/mk/bsd.prefs.mk nor share/mk/bsd.own.mk.

bsd.prefs.mk contains a list of GNU_ARCH.<machine_arch>=xxx
assignments with no entry for <machine_arch>=mipsel.
This should indeed work as bsd.own.mk (which gets included later)
contains a complete table, so bsd.prefs.mk is originally
planned to contain pkgsrc specific additions only.
Now since 1.161, bsd.own.mk only sets MACHINE_GNU_ARCH if
it was not already set before. It gets set to an empty string
by bsd.prefs.mk obviously...

To make it work, I'd add a "mipsel" entry to bsd.prefs.mk for now,
as was done for "mipseb" two weeks ago.
It would be better if a person who understands all the mess in
bsd.prefs.mk would clean it up, to avoid duplicating too much
of bsd.own.mk here. The problem seems to be that MACHINE_GNU_ARCH
is used by Linux/Solaris specific make rules before bsd.own.mk
is included.

best regards
Matthias