illumos gate

When elfsign is built for the host rather than target machine, in usr/src/tools, it uses -I.../uts/common/sys but does not (and cannot, really) get all of the /usr/include headers from there, since install_h has not run. So what it ends up doing is using the system /usr/include (correct) but the source /usr/include/sys (incorrect).

Given that we're building a utility to be executed on the build machine, it should use the system headers for both.

Otherwise, the unspecified mix can and does cause problems.