s3: make unresolved symbols in libs throw errors

s3: make unresolved symbols in libs throw errors

except for the Samba internal plugins unresolved symbol references should not
show up in shared libraries. For historical reasons it's the default behaviour
of linkers to ignore those in shared libs. We use -z defs (alias
--no-undefined) to not ignore them in shared libs.
(cherry picked from commit 7aaec4fe68ce23b0b5880badac378f5ca4386389)