internal/rosa/tamago: disable cgo

This toolchain does not support cgo for the new target, anyway, and disabling it altogether avoids adding a dependency on arm64.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/rosa/tamago.go

@@ -17,6 +17,7 @@ func (t Toolchain) newTamaGo() (pkg.Artifact, string) {
 	), nil, []string{
 		"CC=cc",
 		"GOCACHE=/tmp/gocache",
+		"CGO_ENABLED=0",
 	}, `
 mkdir /work/system # "${TMPDIR}"
 cp -r /usr/src/tamago /work/system