ARC: handle gcc generated __builtin_trap for older compiler

ARC gcc prior to GNU 2018.03 release didn't have a target specific
__builtin_trap() implementation, generating default abort() call.

Implement the abort() call - emulating what newer gcc does for the same,
as suggested by Arnd.
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>

arch/arc/kernel/traps.c

@@ -161,3 +161,11 @@ void do_insterror_or_kprobe(unsigned long address, struct pt_regs *regs)
 
 	insterror_is_error(address, regs);
 }
+
+/*
+ * abort() call generated by older gcc for __builtin_trap()
+ */
+void abort(void)
+{
+	__asm__ __volatile__("trap_s  5\n");
+}