[Libguestfs] [PATCH nbdkit 0/2 v2] golang: Compile against the local nbdkit build.

Version 1 was here: https://www.redhat.com/archives/libguestfs/2020-April/thread.html#00160 Version 2 side-steps the objections to the first patch by using a well-formed alternate nbdkit.pc file and running ordinary pkg-config against it, so any parsing of --cflags etc will be done by pkg-config. The first patch is essentially the same idea as: https://github.com/libguestfs/libnbd/commit/dc87a1a6d6918ac5477e1d6b22599... (which follows on from similar tricks in libguestfs and libvirt). Rich.