Can't build X (unstable and experimental)

[csj <csj@zapo.net>]

I can't build either the unstable or experimental versions of
Debian's xfree86 packages (4.2 and 4.3).  The build ends with the
following error messages:

#BEGIN STDERR
lnx_io.c: In function `KDKBDREP_ioctl_ok':
lnx_io.c:90: error: structure has no member named `rate'
lnx_io.c:98: error: structure has no member named `rate'
lnx_io.c:100: error: structure has no member named `rate'
lnx_io.c:101: error: structure has no member named `rate'
lnx_io.c:102: error: structure has no member named `rate'
make[8]: *** [lnx_io.o] Error 1
make[8]: Leaving directory `/xb/build/debuild/newbuild/XFree86/xfree86-4.3.0/build-tree/xc/programs/Xserver/hw/xfree86/os-support/linux'
make[7]: *** [linux] Error 2
make[7]: Leaving directory `/xb/build/debuild/newbuild/XFree86/xfree86-4.3.0/build-tree/xc/programs/Xserver/hw/xfree86/os-support'
make[6]: *** [all] Error 2
make[6]: Leaving directory `/xb/build/debuild/newbuild/XFree86/xfree86-4.3.0/build-tree/xc/programs/Xserver/hw/xfree86'
make[5]: *** [hw/xfree86] Error 2
make[5]: Leaving directory `/xb/build/debuild/newbuild/XFree86/xfree86-4.3.0/build-tree/xc/programs/Xserver'
make[4]: *** [all] Error 2
make[4]: Leaving directory `/xb/build/debuild/newbuild/XFree86/xfree86-4.3.0/build-tree/xc/programs'
make[3]: *** [all] Error 2
make[3]: Leaving directory `/xb/build/debuild/newbuild/XFree86/xfree86-4.3.0/build-tree/xc'
make[2]: *** [World] Error 2
make[2]: Leaving directory `/xb/build/debuild/newbuild/XFree86/xfree86-4.3.0/build-tree/xc'
make[1]: *** [World] Error 2
make[1]: Leaving directory `/xb/build/debuild/newbuild/XFree86/xfree86-4.3.0/build-tree/xc'
make: *** [stampdir/stamp-build] Error 2
debuild: fatal error at line 469:
dpkg-buildpackage failed!
#END STDERR

Significant is that this is the first time in months that I
haven't been able to build two different or successive versions
of X.  Maybe somebody can identify the error and, if needed,
file a more meaningful bug report.