Handle arch-variant in prebuilt_etc

For cc_binary, changing the handling of version_script to no longer be a
LabelAttribute, which reduces test coverage of that type. Expand
prebuilt_etc to handle arch-variant srcs and correct a bug in
LabelAttribute.

Test: build/bazel/ci/bp2build.sh
Change-Id: I620bc3a43b28c1873f335e30099844ca79ce94c1
diff --git a/etc/prebuilt_etc.go b/etc/prebuilt_etc.go
index 85abf59..408eb51 100644
--- a/etc/prebuilt_etc.go
+++ b/etc/prebuilt_etc.go
@@ -673,8 +673,16 @@
 
 func prebuiltEtcBp2BuildInternal(ctx android.TopDownMutatorContext, module *PrebuiltEtc) {
 	var srcLabelAttribute bazel.LabelAttribute
-	if module.properties.Src != nil {
-		srcLabelAttribute.SetValue(android.BazelLabelForModuleSrcSingle(ctx, *module.properties.Src))
+	for axis, configToProps := range module.GetArchVariantProperties(ctx, &prebuiltEtcProperties{}) {
+		for config, p := range configToProps {
+			props, ok := p.(*prebuiltEtcProperties)
+			if !ok {
+				continue
+			}
+			if props.Src != nil {
+				srcLabelAttribute.SetSelectValue(axis, config, android.BazelLabelForModuleSrcSingle(ctx, *props.Src))
+			}
+		}
 	}
 
 	var filename string