portable: add object_qid.c where required Part of a wider change.

portable: linux: add libmd On some systems libmd isn't explicitly implied, so detect this via pkg-config at configure time. Problem reported by @stsp

portable: configure: split out dependencies Rather than assume all dependencies are required for all programs, split them out. This will make packaging easier, as well as splitting the code to use subprojects. Note that due to the use of config.h semantics, in most cases the got_compat.h header file is now at the top of the .c file it is included in, so that it can handle the system header inclusion properly.

portable: update Makefiles sha1.c -> hash.c

portable: support infrastructure for gotd/gotsh Provide the ability for -portable to continue to compile, until such time that gotd and gotsh have been enabled in -portable.

portable: enable got-read-patch Allow the libexec helper, `got-read-patch` to be compiled, portably.