compiler: don't insert write barriers if we've seen errors
compiler: don't insert write barriers if we've seen errors

The compiler skips the escape analysis pass if it has seen any errors.
The write barrier pass, especially the check-escapes portion, relies
on escape analysis running.  So don't run this pass if there have been
any errors, as it may cause further unreliable error reports.

Change-Id: Ic8c0e86c1b2109d109efa312261b3e84578f18ec
Reviewed-on: https://go-review.googlesource.com/90575
Reviewed-by: Cherry Zhang <d62e63aa42ce272d7b6a5055d97e942b33a34679@google.com>

golang/gofrontend,golang/gofrontend,golang/gofrontend,golang/gofrontend