Make functions static or NOT_USED as appropriate.

src/backend/access/common/Makefile

src/backend/access/common/heapvalid.c

src/backend/commands/copy.c

src/backend/lib/stringinfo.c

src/backend/libpq/auth.c

src/backend/nodes/freefuncs.c

src/backend/optimizer/path/joinrels.c

src/backend/optimizer/plan/setrefs.c

src/backend/parser/parse_clause.c

src/backend/parser/parse_expr.c

src/backend/rewrite/rewriteHandler.c

src/backend/rewrite/rewriteManip.c

src/backend/storage/file/fd.c

src/backend/tcop/postgres.c

src/backend/utils/adt/oracle_compat.c

src/backend/utils/misc/trace.c

src/backend/utils/mmgr/oset.c

src/bin/pg_passwd/pg_passwd.c

src/include/access/valid.h

src/include/lib/stringinfo.h