cmd/compile/internal/ssa: set OFOR bBody.Pos to AST Pos
Assign SSA OFOR's bBody.Pos to AST (*Node).Pos as it is created.
An empty for loop has no other information which may be used to give
correct position information in the resulting executable. Such a for
loop may compile to a single `JMP *self` and it is important that the
location of this is in the right place.
Fixes #30167.
Change-Id: Iec44f0281c462c33fac6b7b8ccfc2ef37434c247
Reviewed-on: https://go-review.googlesource.com/c/go/+/163019
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: David Chase <drchase@google.com>