Please describe the problem:
I've never had problems building with jhbuild (though I've only been using jhbuild for a few weeks now), but in the last couple of days building fails with the following message:

 ...
 gcc -std=gnu99 -DHAVE_CONFIG_H -I. -I.. -I.. -I.. -pthread -DORBIT2=1 -I/opt/usr-jhbuild/include/glib-2.0 -I/opt/usr-jhbuild/lib64/glib-2.0/include -I/opt/usr-jhbuild/include/gconf/2 -I/opt/usr-jhbuild/include/orbit-2.0 -I/opt/usr-jhbuild/include/libxml2 -I/opt/usr-jhbuild/include/dbus-1.0 -I/opt/usr-jhbuild/lib64/dbus-1.0/include -D_REENTRANT -I/opt/usr-jhbuild/include -I/opt/usr-jhbuild/include/glib-2.0 -I/opt/usr-jhbuild/lib64/glib-2.0/include -DDBUS_API_SUBJECT_TO_CHANGE -I/opt/usr-jhbuild/include/glib-2.0 -I/opt/usr-jhbuild/lib64/glib-2.0/include -I/opt/usr-jhbuild/include/hal -I/opt/usr-jhbuild/include/dbus-1.0 -I/opt/usr-jhbuild/lib64/dbus-1.0/include -Wall -Werror -Wchar-subscripts -Wmissing-declarations -Wmissing-prototypes -Wnested-externs -Wpointer-arith -Wno-strict-aliasing -Wno-sign-compare -DXDG_PREFIX=_gnome_vfs_xdg -DDBUS_API_SUBJECT_TO_CHANGE -D_FILE_OFFSET_BITS=64 -D_BSD_SOURCE -D_LARGEFILE64_SOURCE -D_POSIX_PTHREAD_SEMANTICS -D_REENTRANT -DG_DISABLE_DEPRECATED -DGNOME_VFS_PREFIX=\"/opt/usr-jhbuild\" -DGNOME_VFS_BINDIR=\"/opt/usr-jhbuild/bin\" -DGNOME_VFS_DATADIR=\"/opt/usr-jhbuild/share\" -DGNOME_VFS_LIBDIR=\"/opt/usr-jhbuild/lib64\" -DGNOME_VFS_LOCALEDIR=\"/opt/usr-jhbuild/share/locale\" -DGNOME_VFS_SYSCONFDIR=\"/opt/usr-jhbuild/etc\" -DG_LOG_DOMAIN=\"libgnomevfs\" -g -O0 -MT gnome-vfs-ace.lo -MD -MP -MF .deps/gnome-vfs-ace.Tpo -c gnome-vfs-ace.c  -fPIC -DPIC -o .libs/gnome-vfs-ace.o
cc1: warnings being treated as errors
In file included from /opt/usr-jhbuild/include/glib-2.0/glib/gthread.h:32,
                 from /opt/usr-jhbuild/include/glib-2.0/glib/gasyncqueue.h:30,
                 from /opt/usr-jhbuild/include/glib-2.0/glib.h:32,
                 from gnome-vfs-ace.h:28,
                 from gnome-vfs-ace.c:26:
/opt/usr-jhbuild/include/glib-2.0/glib/gutils.h:320: warning: C99 inline functions are not supported; using GNU89
/opt/usr-jhbuild/include/glib-2.0/glib/gutils.h:320: warning: to disable this warning use -fgnu89-inline or the gnu_inline function attribute
/opt/usr-jhbuild/include/glib-2.0/glib/gutils.h:334: warning: C99 inline functions are not supported; using GNU89
/opt/usr-jhbuild/include/glib-2.0/glib/gutils.h:347: warning: C99 inline functions are not supported; using GNU89
/opt/usr-jhbuild/include/glib-2.0/glib/gutils.h:366: warning: C99 inline functions are not supported; using GNU89
/opt/usr-jhbuild/include/glib-2.0/glib/gutils.h:374: warning: C99 inline functions are not supported; using GNU89
/opt/usr-jhbuild/include/glib-2.0/glib/gutils.h:391: warning: C99 inline functions are not supported; using GNU89
/opt/usr-jhbuild/include/glib-2.0/glib/gutils.h:400: warning: C99 inline functions are not supported; using GNU89
In file included from /opt/usr-jhbuild/include/glib-2.0/glib/gasyncqueue.h:30,
                 from /opt/usr-jhbuild/include/glib-2.0/glib.h:32,
                 from gnome-vfs-ace.h:28,
                 from gnome-vfs-ace.c:26:
/opt/usr-jhbuild/include/glib-2.0/glib/gthread.h:334: warning: C99 inline functions are not supported; using GNU89
make[3]: *** [gnome-vfs-ace.lo] Error 1
make[3]: Leaving directory `/usr/src/jhbuild-sources/gnome-vfs/libgnomevfs'

The output of `gcc -v' is:

[02:58][jose@sweety:/usr/src/jhbuild-sources/gnome-vfs]$ gcc -v
Using built-in specs.
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --enable-languages=c,c++,fortran,objc,obj-c++,treelang --prefix=/usr --enable-shared --with-system-zlib --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --enable-nls --with-gxx-include-dir=/usr/include/c++/4.2 --program-suffix=-4.2 --enable-clocale=gnu --enable-libstdcxx-debug --enable-objc-gc --enable-mpfr --disable-libmudflap --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 4.2.3 (Debian 4.2.3-2)

Steps to reproduce:
1. Remove gnome-vfs directory from jhbuild source directory
2. run `jhbuild buildone gnome-vfs'
3. Compile error is produced


Actual results:
Compile error is produced

Expected results:
Build would continue with success (as it has in the past)

Does this happen every time?
Yes

Other information:
My system is an updated GNU/Linux (Debian) Lenny/Sid (unstable)