arc: Use intrinsics for __builtin_mul_overflow ()

arc: Use intrinsics for __builtin_mul_overflow ()

This patch handles both signed and unsigned builtin multiplication
overflow.

Uses the "mpy.f" instruction to set the condition codes based on the
result.  In the event of an overflow, the V flag is set, triggering a
conditional move depending on the V flag status.

For example, set "1" to "r0" in case of overflow:

        mov_s   r0,1
        mpy.f   r0,r0,r1
        j_s.d   [blink]
        mov.nv  r0,0

gcc/ChangeLog:

	* config/arc/arc.md (<su_optab>mulvsi4): New define_expand.
	(<su_optab>mulsi3_Vcmp): New define_insn.

Signed-off-by: Luis Silva <luiss@synopsys.com>