runtime: print pc with fp/sp in traceback

If we're in a situation where printing the fp and sp in the traceback
is useful, it's almost certainly also useful to print the PC.

Change-Id: Ie48a0d5de8a54b5b90ab1d18638a897958e48f70
Reviewed-on: https://go-review.googlesource.com/45210
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>

src/runtime/traceback.go

@@ -433,7 +433,7 @@ func gentraceback(pc0, sp0, lr0 uintptr, gp *g, skip int, pcbuf *uintptr, max in
 					print(" +", hex(frame.pc-f.entry))
 				}
 				if g.m.throwing > 0 && gp == g.m.curg || level >= 2 {
-					print(" fp=", hex(frame.fp), " sp=", hex(frame.sp))
+					print(" fp=", hex(frame.fp), " sp=", hex(frame.sp), " pc=", hex(frame.pc))
 				}
 				print("\n")
 				nprint++