We can just set GREP and SED in the configure command instead of fixing up
the paths using sed afterwards. This makes the build more robust (and we're
currently preparing a change of the host staging dirs in LEDE that might
break this otherwise).

Signed-off-by: Matthias Schiffer <mschiffer@universe-factory.net>

Switch to xz tarball

Signed-off-by: Daniel Engberg <daniel.engberg.lists@pyret.net>

GNU libtool is used to ease the usage of shared libraries in Makefiles.

The new package libtool-bin contains the script libtoolize which is used
to prepare a package to use libtool.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>