libtool: Fix tools path issues

If for example you build on a machine with /bin/grep, then restore that sstate
onto a machine with /usr/bin/grep, things will fail. Simply don't bother
hardcoding paths.

This was lost during the libtool upgrade:

http://git.yoctoproject.org/cgit.cgi/poky/diff/meta/recipes-devtools/libtool/libtool/avoid_absolute_paths_for_general_utils.patch?id=d4e1862453b2a4c12400de0f43f08a9871a4de60



since the path to the files changed. This restores the previous behaviour.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>