runtime: always build panic32.go
runtime: always build panic32.go

Avoids problems with arm64 ILP32 mode.  We might want to handle that
mode better in general, but always building panic32.go is simple and
fixes the build.

Change-Id: I57c0d2ba51176be36ab8020e60ee62d4aa397e28
Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/192723
Reviewed-by: Cherry Zhang <d62e63aa42ce272d7b6a5055d97e942b33a34679@google.com>

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