build.sh vs. read-only fs netbsd-7

[Louis Guillaume <louis%zabrico.com@localhost>]

Hi!

I just updated my src tree to netbsd-7. After clearing everything away 
from /usr/obj, I attempted a build. Here are some details...

  o amd64 system
  o netbsd-7 branch as of last night
  o /usr/src is mounted read-only
  o nothing special in mk.conf
  o recent netbsd-6 builds worked fine


$ ./build.sh -u -U -T /usr/obj/TOOLDIR.amd64 -O /usr/obj tools

(worked fine)

$ ./build.sh -u -U -T /usr/obj/TOOLDIR.amd64 -O /usr/obj release

This one fails here...

#       lex  backend//usr/src/external/gpl3/gcc/dist/gcc/gengtype-lex.c
/usr/obj/TOOLDIR.amd64/bin/nblex 
-o/usr/src/external/gpl3/gcc/dist/gcc/gengtype-lex.c 
/usr/src/external/gpl3/gcc/dist/gcc/gengtype-lex.l
nblex: could not create /usr/src/external/gpl3/gcc/dist/gcc/gengtype-lex.c


Why's it writing to /usr/src/ rather than somewhere in /usr/obj?

Any help would be great. Thanks,

Louis