BUILD: fd: disguise the fd_set_nonblock/cloexec result

BUILD: fd: disguise the fd_set_nonblock/cloexec result

We thought that we could get rid of some DISGUISE() with commit a80e4a354
("MINOR: fd: add functions to set O_NONBLOCK and FD_CLOEXEC") thanks to
the calls being in a function but that was without counting on Coverity.
Let's put it directly in the function since most if not all callers don't
care about this result.