s3-build: Provide a run-time shim to work around duplicate symbols

s3-build: Provide a run-time shim to work around duplicate symbols

The become_root() and similar 'smbd' functions that are used widely in
Samba libraries had 'dummy' copies in dummysmbd.c and dummyroot.c.

These have been replaced by a runtime plugin mechanim, which ensures
that standlone binaries still do nothing, while in smbd the correct
function is used.

This avoids having these as duplicate symbols in the smbd binary,
which can cause unpredictable behaviour.

Andrew Bartlett

Signed-off-by: Andrew Tridgell <tridge@samba.org>