Fix incompatible struct declarations.

Fix incompatible struct declarations.

* doc/libtool.texi (Dlpreopening): Remove broken documentation
of lt_dlsymbol and lt_dlsymlist.  Document typedef lt_dlsymlist
and symbol lt_preloaded_symbols according to the implementation.
* tests/demo/dlmain.c (lt_symlist): Make struct anonymous ...
(lt_dlsymlist): ... and typedef to this name.
(lt_preloaded_symbols, main): Adjust.
* tests/pdemo/longer_file_name_dlmain.c: Likewise.

Signed-off-by: Ralf Wildenhues <Ralf.Wildenhues@gmx.de>