ARC: unbork buildroot build

crt1.S -> include sysdep.h -> include sysnum.h

In multistage gcc build, Buildroot happens to build crt1.S before
sysnum.h is generated. So break the above include chain and opencode the
ENTRY/END macros.

Reported-by: Anton Kolesov <akolesov@synopsys.com>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>