This makes the rounding bug fix in math/big for issue 14651 available
to the compiler.
- changes to cmd/compile/internal/big fully automatic via script
- added test case for issue
- updated old test case with correct test data
Fixes#14651.
Change-Id: Iea37a2cd8d3a75f8c96193748b66156a987bbe40
Reviewed-on: https://go-review.googlesource.com/20818
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
