Discussions on src-committers with alfred and bde pointed out that

Discussions on src-committers with alfred and bde pointed out that
the "do-nothing" versions of __RCSID(), __RCSID_SOURCE(), __SCCSID(),
and __COPYRIGHT() were not strictly correct.  They should not expand
into [nothing], because the ';' which follows them would then cause
a syntax error (in a strict C compiler, if not gcc...).

So, change the do-nothing versions of those macros to use the
'struct __hack' tactic, as was already used with __FBSDID().

Approved by:	discussions with bde
MFC after:	1 week