Add additional includes needed on some platforms.

contrib/btree_gist/btree_numeric.c

contrib/btree_gist/btree_utils_num.h

contrib/btree_gist/btree_utils_var.c

src/backend/executor/nodeHash.c

src/interfaces/libpq/fe-auth.c

src/interfaces/libpq/fe-print.c

src/interfaces/libpq/fe-protocol2.c

src/interfaces/libpq/fe-secure.c

src/port/strdup.c

src/timezone/pgtz.c

src/timezone/strftime.c

src/tutorial/funcs_new.c