test: only require issue11674 errors with gc compiler

The gofrontend code sees that the denominator is not zero,
so it computes the values. Dividing zero by a non-zero value
produces zero. The language spec doesn't require any of these
cases to report an error, so make the errors compiler-specific.

Change-Id: I5ed759a3121e38b937744d32250adcbdf2c4d3c2
Reviewed-on: https://go-review.googlesource.com/c/go/+/278117


Trust: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>