Some further information:

I compiled gas.new from -current, and it had the same problems
(whatever they may be).

I also tried using egcs.  It generates code that falls over heavily.
libc/arch/arm32/softfloat.c blows up all over the place, and a newly
compiled tosrt(1) generates incorrect output (causing other parts of
the build to lose, amusingly enough).  Definitely not stable enough
for general use.

I'm going to let it rebuild the world with gcc 2.7 and see if anything
else blows up.