build: force use of ltmain.sh from libtool 2.2.6b

build: force use of ltmain.sh from libtool 2.2.6b

Don Ward:

"The supplied version of ltmain.sh does not handle interlibrary
dependencies on Windows. I have attached a diff file showing
the slight differences between the ltmain.sh in the tarball
(2.2.6b Debian-2.2.6b-2ubuntu1, which fails) and the ltmain.sh
downloaded from packages.debian.org  (plain 2.26b).  It looks
like it was broken in Ubuntu 2.2.6a-3 (change log says "Don't
pull in depedency libs when linking a binary"). GNU Radio builds
ok if I run ./bootstrap locally."

JMC: This file (ltmain.sh) has not previously been under version
control and would be copied over (or symlinked) by the bootstrap
process. With a version now in the repository, we'll need to
ensure it stays fresh, likely at the same time we check for
updated config.guess and config.sub files.