This adds the three subdirecotries to the build, and fixes missing
includes and libs by referring to ../ as needed.  Now it looks like
everything builds.

After building, the following files remain in the source tree:

    patches/buildroot/0001-netsnmp-config-to-reduce-footprint.patch
    userspace/rootfs_override/etc/snmp/
    userspace/rootfs_override/usr/

The first one is likely needed for building builroot, but this commit
doesn't do anything about it.  The other directories are stuff that should
be installed: etc/snmp/snmpd.conf and usr/lib/{libieee8021{,q}bridge.so
Signed-off-by: Alessandro Rubini <rubini@gnudd.com>

This make the mandatory steps to bring compilation to a succesfull end:
  - it adds the missing -I and -L to Makefiles so they pick from ../sth
  - it removes building spll_dbg_proxy because there is no such subdir
  - it removes installation if libminipc.so and libwripc.so (they don't exist)
Signed-off-by: Alessandro Rubini <rubini@gnudd.com>

Signed-off-by: Alessandro Rubini <rubini@gnudd.com>

Conflicts:

	.gitmodules

(this is still not building)

This is cherry-picked, but it has a conflict in userspace/Makefile.
I chose to overwrite it with the version back then, which uses
$(SUBDIRS) in all rules to remove some duplication.
Signed-off-by: Alessandro Rubini <rubini@gnudd.com>

Signed-off-by: Alessandro Rubini <rubini@gnudd.com>

Signed-off-by: Alessandro Rubini <rubini@gnudd.com>