tools/libtool: bump to 2.4.6

tools/libtool: bump to 2.4.6

This updates libtool to its current release, from 2015.  Current patches
were renumbered and given a description text.  The fix in
160-passthrough-ssp.patch is no longer needed.

A patch to speed up build was cherry-picked, and another openwrt
specific patch was needed to not use quotes in $(SHELL), to acommodate
our "SHELL=/usr/bin/env bash" usage.

The already present call to ./bootstrap ensures that generated files are
refreshed, so the patches are applied only to their sources.  Also, that
bootstrap call was adjusted to run at the appropriate time when QUILT=1.

References below are relevant commits to upstream libtool
regarding some of the changes to patches.

This commit is being reapplied after previous revertion, and after some editing.
The fix for the issue that prompted reverting is the parent of this commit.

Ref: 435cb8d71 ("libtoolize: simplify runtime by substituting pkgauxdir")
Ref: 3cf11cfe2 ("libtoolize: rewritten over funclib.sh instead of general.m4sh")
Signed-off-by: Eneas U de Queiroz <cotequeiroz@gmail.com>
Signed-off-by: Sebastian Kemper <sebastian_ml@gmx.net>
[refactored to simplify patch changes, expanded patches, added upstream references]
Signed-off-by: Michael Pratt <mcpratt@pm.me>