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.

Signed-off-by: Eneas U de Queiroz <cotequeiroz@gmail.com>

tools/libtool/patches/110-dont-use-target-dir-for-relinking.patch

@@ -1,20 +1,33 @@
---- a/libltdl/config/ltmain.m4sh
-+++ b/libltdl/config/ltmain.m4sh
-@@ -6120,7 +6120,6 @@ func_mode_link ()
- 	       test "$hardcode_direct_absolute" = no; then
- 	      add="$libdir/$linklib"
- 	    elif test "$hardcode_minus_L" = yes; then
--	      add_dir="-L$libdir"
- 	      add="-l$name"
- 	    elif test "$hardcode_shlibpath_var" = yes; then
- 	      case :$finalize_shlibpath: in
---- a/libltdl/config/ltmain.sh
-+++ b/libltdl/config/ltmain.sh
-@@ -6907,7 +6907,6 @@ func_mode_link ()
- 	       test "$hardcode_direct_absolute" = no; then
- 	      add="$libdir/$linklib"
- 	    elif test "$hardcode_minus_L" = yes; then
--	      add_dir="-L$libdir"
- 	      add="-l$name"
- 	    elif test "$hardcode_shlibpath_var" = yes; then
+From 375833af93999f8b0a747c8a1dfa3ec8d347743d Mon Sep 17 00:00:00 2001
+From: Eneas U de Queiroz <cotequeiroz@gmail.com>
+Date: Tue, 20 Jul 2021 16:52:37 -0300
+Subject: openwrt: don't use target dir for relinking
+
+This was originally commited to openwrt by Jo-Philipp Wich
+<jow@openwrt.org>.
+
+(adjusted to v2.4.6)
+Signed-off-by: Eneas U de Queiroz <cotequeiroz@gmail.com>
+
+--- a/build-aux/ltmain.in
++++ b/build-aux/ltmain.in
+@@ -6434,13 +6434,13 @@ func_mode_link ()
+ 	    add_dir=
+ 	    add=
+ 	    # Finalize command for both is simple: just hardcode it.
+-	    if test yes = "$hardcode_direct" &&
+-	       test no = "$hardcode_direct_absolute"; then
+-	      add=$libdir/$linklib
+-	    elif test yes = "$hardcode_minus_L"; then
++	    if test "$hardcode_direct" = yes &&
++	       test "$hardcode_direct_absolute" = no; then
++	      add="$libdir/$linklib"
++	    elif test "$hardcode_minus_L" = yes; then
+ 	      add_dir=-L$libdir
+-	      add=-l$name
+-	    elif test yes = "$hardcode_shlibpath_var"; then
++	      add="-l$name"
++	    elif test "$hardcode_shlibpath_var" = yes; then
  	      case :$finalize_shlibpath: in
+ 	      *":$libdir:"*) ;;
+ 	      *) func_append finalize_shlibpath "$libdir:" ;;