tools/nolibc: remove local definitions of O_* flags for open/fcntl

The historic nolibc code did not include asm/fcntl.h and had to define
the various O_RDWR etc macros in each arch-specific file (since such
values differ between certain archs). This was found at least once to
induce bugs due to wrong definitions. Let's get rid of all of them and
include asm/nolibc.h from sys.h instead. This was verified to work
properly on all supported architectures.

Signed-off-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>