runtime: print faulting instruction on a SIGFPE

Just like SIGILL, it might be useful to see what the instruction
that generated the SIGFPE is.

Update golang#39816

Change-Id: I8b2ff692998f0b770289339537dceab96b09d1ee
Reviewed-on: https://go-review.googlesource.com/c/go/+/239999
Run-TryBot: Keith Randall <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>

Author: randall77

src/runtime/signal_unix.go

@@ -616,7 +616,7 @@ func sighandler(sig uint32, info *siginfo, ctxt unsafe.Pointer, gp *g) {
 		print("signal arrived during cgo execution\n")
 		gp = _g_.m.lockedg.ptr()
 	}
-	if sig == _SIGILL {
+	if sig == _SIGILL || sig == _SIGFPE {
 		// It would be nice to know how long the instruction is.
 		// Unfortunately, that's complicated to do in general (mostly for x86
 		// and s930x, but other archs have non-standard instruction lengths also).