make distclean fails for libstdc++-v3 and srcdir==objdir

[Gerald Pfeifer]

If I build with srcdir==objdir (on all my platforms, the following is on
sparc-sun-solaris2.8), make distclean fails for libstdc++-v3:

  rm -f Makefile tests_flags mkcheck
  rm -f config.cache config.log stamp-h stamp-h[0-9]*
  make "AR_FLAGS=rc" "CC_FOR_BUILD=gcc" [...]
  make: Fatal error: Don't know how to make target `multi-clean'
  Current working directory /sw/test/gcc/cvs/sparc-sun-solaris2.8/libstdc++-v3
  *** Error code 1
  make: Fatal error: Command failed for target `mostlyclean-multi'

In general it seems, that I'm the first to ever test libstdc++-v3 with
srcdir==objdir? Until Alexandre's patch for my report earlier this week
we wouldn't even build, and `make install` does still fail (though I have
to test a suggestion by Alexandre on how to fix that).

Gerald
-- 
Gerald "Jerry" pfeifer@dbai.tuwien.ac.at http://www.dbai.tuwien.ac.at/~pfeifer/