Check only regular files, not devices, for lalibs.

Check only regular files, not devices, for lalibs.

* libltdl/config/ltmain.m4sh (functions func_lalib_p)
(func_lalib_unsafe_p): Only read regular files and not device
files.  Avoids blocking libtool executing gdb, when a
pseudo-terminal device /dev/pts/NN is given as one of the
arguments to gdb, as in:
libtool --mode=execute gdb -q -nw -i mi -tty /dev/pts/4 prog

Signed-off-by: Stas Maximov <smaximov@ieee.org>
Signed-off-by: Ralf Wildenhues <Ralf.Wildenhues@gmx.de>