We shouldn't be using the os wrappers from os code - we can use libc directly.
This patch replaces wrapper calls with libc calls.

It turns out that os_sigio_async had only one caller, which was in startup.c,
so that function is moved there and its name changed.
Signed-off-by: Jeff Dike <jdike@addtoit.com>
Cc: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>