Add debian/patches/0002-libtool-modification.patch and fix for cross building.
I have two commits for experimental.
- debian/patches/0002-libtool-modification.patch: New.
This is to make sure apply upstream GnuPG modification of libtool effective, a backport from upstream.
A change for debian/rules for cross building (by adding CC_FOR_BUILD) is needed when the host has Windows emulation (semi hosted environment for Windows). This would be important if we consider enable testing on semi hosted environment.