arch: define weak abort()

gcc toggle -fisolate-erroneous-paths-dereference (default at -O2
onwards) isolates faulty code paths such as null pointer access, divide
by zero etc.  If gcc port doesnt implement __builtin_trap, an abort() is
generated which causes kernel link error.

In this case, gcc is generating abort due to 'divide by zero' in
lib/mpi/mpih-div.c.

Currently 'frv' and 'arc' are failing.  Previously other arch was also
broken like m32r was fixed by commit d22e3d69ee ("m32r: fix build
failure").

Let's define this weak function which is common for all arch and fix the
problem permanently.  We can even remove the arch specific 'abort' after
this is done.

Link: http://lkml.kernel.org/r/1513118956-8718-1-git-send-email-sudipm.mukherjee@gmail.com
Signed-off-by: Sudip Mukherjee <sudipm.mukherjee@gmail.com>
Cc: Alexey Brodkin <Alexey.Brodkin@synopsys.com>
Cc: Vineet Gupta <Vineet.Gupta1@synopsys.com>
Cc: Sudip Mukherjee <sudipm.mukherjee@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/exit.c

@@ -1755,3 +1755,11 @@ Efault:
 	return -EFAULT;
 }
 #endif
+
+__weak void abort(void)
+{
+	BUG();
+
+	/* if that doesn't kill us, halt */
+	panic("Oops failed to kill thread");
+}