Use typeof everywhere instead of compiler specific spellings

Use typeof everywhere instead of compiler specific spellings

We define typeof ourselves as __typeof__ if it does not exist.  So
let's actually use that for consistency.  The meson/autoconf checks
for __builtin_types_compatible_p still use __typeof__ though, because
there we have not redefined it.

Author: Jelte Fennema-Nio <postgres@jeltef.nl>
Discussion: https://www.postgresql.org/message-id/flat/CAGECzQR21OnnKiZO_1rLWO0-16kg1JBxnVq-wymYW0-_1cUNtg@mail.gmail.com