fd-util: Move RAW_O_LARGEFILE definition to fd-util.h

fd-util: Move RAW_O_LARGEFILE definition to fd-util.h

This is not something that comes from glibc, but which we invent
ourselves. As such, it should not be part of our overrides of glibc
headers, but instead should be part of one of our own headers, so
let's move it to fd-util.h.

Follow up for 194a690181c4857542a094d19f5808f8f4032ed9