runtime: fix TestCallersNilPointerPanic

The expected result of TestCallersNilPointerPanic has changed in
GoLLVM.  This CL makes some elements of the expected result optional
so that this test passes in both gccgo and GoLLVM.

Change-Id: I8a909266ead0b99062da075bbf645bade95a1ea5
Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/230138
Reviewed-by: Ian Lance Taylor <iant@golang.org>
1 file changed