The value EAGAIN is allowed by POSIX to be the same as EWOULDBLOCK, but this is
not guaranteed. Thus on some systems (e.g. glibc Linux), we get a warning that
the logical OR is being performed on two expressions of the same type. We can
not get rid of this test in case any system defines these as unique values.

Suggested-by: Dave Reisner
Signed-off-by: Allan McRae <allan@archlinux.org>