Duplicate symbols now banned in master (top level build)

[Andrew Bartlett]

The top level build now has checks for duplicate symbols, even where
they are in different shared libraries.  The test checks to see if they
are linked into the same binary.

Duplicate symbols have been a big issue in the Samba4 build for a long
time, and now that we are finally rid of them across the whole top level
build, I've added a check in 'make test' to ensure it stays that way for
a Samba 4.0 release.  

This check code is activated via the --dup-symbol-check that has been
added to the default 'make test' invocation of waf.  If for some reason
you have configured with --enable-developer on a system that fails to
run the tools on which this test is based, you can edit the Makefile.

Additionally, this test is not run on the build farm.

If you do have reason to disable this locally, please work with Tridge
or I to understand the versions of ldd and readelf that fail, so we can
add a configure test.

To avoid duplicate symbols, typically the subsystem containing those
symbols needs to become a library, or be placed into one.  I'm quite
happy to help with these details if folks get stuck. 

Thanks,

Andrew Bartlett
-- 
Andrew Bartlett                                http://samba.org/~abartlet/
Authentication Developer, Samba Team           http://samba.org