Include version.c from build dir in preference to source dir

Include version.c from build dir in preference to source dir

This should fix out-of-source-tree builds from a tarball, which
otherwise would use the autogenerated $(objdir)/version.c for building
the library, but the pre-packaged $(srcdir)/version.c for the
executable. This is because the latter was included directly from main.c
by #include "version.c". By changing to #include <main.c> instead, we get
to use the new auto-generated one instead if anything's been changed.

Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>