If a failure occurs in SSA processing, we always report the
last line of the function we're compiling.  Modify the callbacks
from SSA to the GC compiler so we can pass a line number back
and use it in Fatalf.

Change-Id: Ifbfad50d5e167e997e0a96f0775bcc369f5c397e
Reviewed-on: https://go-review.googlesource.com/18599
Run-TryBot: Keith Randall <khr@golang.org>
Reviewed-by: David Chase <drchase@google.com>