waf: added --symbol-check option

waf: added --symbol-check option

this adds checking of the symbols in all our object files, libraries
and syslibs. It will form the basis in future for a lot more checks,
but for now it just checks basic rules like not allowing us to use
symbols that are in system libs.

Currently this is enabled only if you use the --symbol-check option,
(or use make with SYMBOLCHECK=1) but I intend to make this always
enabled once it has had more testing.

Pair-Programmed-With: Andrew Bartlett <abartlet@samba.org>