Platform: Retarget: Add __stderr definition

Retarget only defines __stdout for armclang. In some cases, if
__stderr is not defined, stdio_streams.o is automatically added
at link step, which conflicts with our default retarget.

Change-Id: I83563220a9d320e818e404b2114adf63a532daa5
Signed-off-by: Gabor Abonyi <gabor.abonyi@arm.com>
1 file changed