tools/elfutils: do not use libtool for all subdirectories

tools/elfutils: do not use libtool for all subdirectories

Importing gnulib in order to have a local portable library
to link against for missing functions currently requires
using libtool to produce the libgnu.la library.

Ideally, linking would be simple if the rest of the libraries
built by elfutils were also built using libtool, as linking
them together would not require any manipulations of library paths.

However, upstream elfutils does not support building the libraries
statically with libtool, so using libtool comes at the cost
of creating a huge patch to introduce that functionality.

For building on macOS, it turns out that libgnu.la is only needed
for building the binaries, and that just one or two objects from libgnu
are needed to build the libraries, so in this case, it would be simple
to add the specific non-libtool-wrapped library and objects
to the link paths as needed, rather than use libtool to link
the libtool wrappers, which greatly reduces the need to patch.

Not using libtool also makes the original Makefile definitions for LIBADD
once again be the right ones to use. However, to be portable,
for libdw the wildcard function needs to be used in order to exclude
special archive members like "__.SYMDEF" which are not compiled objects
because some BSD-like versions of ar include that metadata in the list,
or because the library included may have objects from another subdirectory.
Also, the rest of the subdirectories have custom "LDLIBS" variables
meant for building shared objects only, so define the LIBADD variables
with objects from those existing definitions so that when building only
the static versions of the libraries, those objects can still be included.

Signed-off-by: Michael Pratt <mcpratt@pm.me>
Link: https://github.com/openwrt/openwrt/pull/15690
Signed-off-by: Robert Marko <robimarko@gmail.com>