make distcheck problem

[Lars Hecking]

 I have the following in a Makefile.am:

if BUILD_SRC_BEOS_SUBDIR
d_beos = beos
endif
SUBDIRS = $(d_beos)

 where BUILD_SRC_BEOS_SUBDIR is from an AM_CONDITIONAL in configure.in.
 BUILD_SRC_BEOS_SUBDIR is not defined because I'm not building on BeOS.
 The directory structure is

 top level
 top level/src
 top level/src/beos

 If I run make distcheck in the top level directory, it bombs out at
 one point because the beos subdir doesn't exist. Is this a bug in
 automake? Is there any way to work around it? I am not running on 

[...]
make[2]: Entering directory `/home/lhecking/gnuplot/gnuplot-3.8k.0/_build/src'
list='beos'; for subdir in $list; do \
  if test "$subdir" = .; then :; else \
    test -d "../gnuplot-3.8k.0/src/$subdir" \
    || mkdir "../gnuplot-3.8k.0/src/$subdir" \
    || exit 1; \
    (cd $subdir && \
      make  \
        top_distdir="../../gnuplot-3.8k.0" \
        distdir="../../gnuplot-3.8k.0/src/$subdir" \
        distdir) \
      || exit 1; \
  fi; \
done
/bin/bash: cd: beos: No such file or directory
make[2]: *** [distdir] Error 1
make[2]: Leaving directory `/home/lhecking/gnuplot/gnuplot-3.8k.0/