symlinked libltdl and aclocal

[Ralf Wildenhues]

Symlinking libltdl into a project (as in)
  libtoolize --ltdl

is pretty stupid when later on aclocal decides it needs to run in
libltdl/ -- it'll try to write in the aclocal.m4 file that can be
reached through the symlink, instead of removing the symlink before
writing.  This may happen in the non-subpackage case (whenever that'll
work), but I believe it can also trigger when AC_CONFIG_MACRO_DIR is
shared between the packages.

Bug in aclocal?  I think so.

Cheers,
Ralf