test/fixedbugs: require cgo for issue10607.go

test/fixedbugs: require cgo for issue10607.go

This test passes "-linkmode=external" to 'go run' to link the binary
using the system C linker.

CGO_ENABLED=0 explicitly tells cmd/go not to use the C toolchain,
so the test should not be run in that configuration.

Updates #46330.

Change-Id: I16ac66aac91178045f9decaeb28134061e9711f7
Reviewed-on: https://go-review.googlesource.com/c/go/+/522495
Reviewed-by: Heschi Kreinick <heschi@google.com>
Reviewed-by: Than McIntosh <thanm@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Bryan Mills <bcmills@google.com>
Run-TryBot: Bryan Mills <bcmills@google.com>