do_build.sh: export OPENXT_GIT_PROTOCOL for xctools

Add export of OPENXT_GIT_PROTOCOL for xctools build scripts

OXT-46
pkg-xc{tools,switcher}/build: Add OPENXT_GIT_PROTOCOL

Add OPENXT_GIT_PROTOCOL to git URIs in xctools build scripts.

OXT-46
Merge pull request #41 from bennettj1087/oxt-46

[OXT-46] openxt: Add missing protocol string to git URIs in xctools build scripts