docs: @file and @option markup fixes.

docs: @file and @option markup fixes.

* doc/libtool.texi (Creating object files, Linking libraries)
(Linking executables, Link mode, Finish mode, Autoconf macros)
(Using Automake, Inter-library dependencies, Dlpreopening)
(Linking with dlopened modules, Finding the dlname)
(Libltdl interface, Test descriptions, Multiple dependencies):
Add @option where needed, replace @samp with @file as
appropriate.

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