Get rid of trailing semicolons in C macro definitions.

Get rid of trailing semicolons in C macro definitions.

Writing a trailing semicolon in a macro is almost never the right thing,
because you almost always want to write a semicolon after each macro
call instead.  (Even if there was some reason to prefer not to, pgindent
would probably make a hash of code formatted that way; so within PG the
rule should basically be "don't do it".)  Thus, if we have a semi inside
the macro, the compiler sees "something;;".  Much of the time the extra
empty statement is harmless, but it could lead to mysterious syntax
errors at call sites.  In perhaps an overabundance of neatnik-ism, let's
run around and get rid of the excess semicolons whereever possible.

The only thing worse than a mysterious syntax error is a mysterious
syntax error that only happens in the back branches; therefore,
backpatch these changes where relevant, which is most of them because
most of these mistakes are old.  (The lack of reported problems shows
that this is largely a hypothetical issue, but still, it could bite
us in some future patch.)

John Naylor and Tom Lane

Discussion: https://postgr.es/m/CACPNZCs0qWTqJ2QUSGJ07B7uvAvzMb-KbG2q+oo+J3tsWN5cqw@mail.gmail.com