sys/file.h: Allow inclusion when compiling for a strict namespace

Although not part of the standard, this file is sometimes included with
-D_POSIX_C_SOURCE=<value> or -D_XOPEN_SOURCE=<value>. Limit those
sturctures that use types hidden by __BSD_VISIBLE to when they are
visible.

PR: 259975, 234205
Sponsored by: Netflix

(cherry picked from commit a2b53e53a3f38dd89b64500a2d2a1727baffe4f9)