autotools: inherit LIBTOOL_PATCH for host packages

When FOO_LIBTOOL_PATCH is defined, assume that the same value should
be used for HOST_FOO_LIBTOOL_PATCH.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>