Added the ability to patch ltmain.sh based on version

There are two versions of ltmain.sh in use in the buildroot system, 1.5.x and
2.2.x. buildroot-libtool.patch would only patch 1.5.x, which meant that for
2.2.x, a separate patch for the affected package had to be maintained. Modified
Makefile.autotools.in to check the version of ltmain.sh and apply the correct
patch.

Signed-off-by: Martin Banky <Martin.Banky@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>