ARC: LIB: MWDT: add stdout hooks, timespec header

ARC MWDT toolchain misses stdout hooks implementation and
itimerspec structure in timespec header. Let's add them in
arcmwdt compatibility layer.

The implementation was inspired by libc-hooks.c for NEWLIB.

Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
Signed-off-by: Evgeniy Paltsev <PaltsevEvgeniy@gmail.com>