Handle product_variable asflag for cc_object.

cc_object crtbrand sets product_variable.platform_sdk_version.asflag
and will not compile correctly within mixed builds without it.

Only handles product_variables that expand product variables.

Bug: 181794963
Test: ~/aosp/build/bazel/scripts/milestone-2/demo.sh full
Change-Id: I293fcb18032aa51f63bb7b3de94abd6d1ec38180

cc/object.go

@@ -106,6 +106,7 @@ type bazelObjectAttributes struct {
 	Srcs               bazel.LabelList
 	Deps               bazel.LabelList
 	Copts              bazel.StringListAttribute
+	Asflags            []string
 	Local_include_dirs []string
 }
 
@@ -150,6 +151,7 @@ func ObjectBp2Build(ctx android.TopDownMutatorContext) {
 	var srcs []string
 	var excludeSrcs []string
 	var localIncludeDirs []string
+	var asFlags []string
 	for _, props := range m.compiler.compilerProps() {
 		if baseCompilerProps, ok := props.(*BaseCompilerProperties); ok {
 			copts.Value = baseCompilerProps.Cflags
@@ -171,6 +173,23 @@ func ObjectBp2Build(ctx android.TopDownMutatorContext) {
 		}
 	}
 
+	productVariableProps := android.ProductVariableProperties(ctx)
+	if props, exists := productVariableProps["Asflags"]; exists {
+		// TODO(b/183595873): consider deduplicating handling of product variable properties
+		for _, prop := range props {
+			flags, ok := prop.Property.([]string)
+			if !ok {
+				ctx.ModuleErrorf("Could not convert product variable asflag property")
+				return
+			}
+			// TODO(b/183595873) handle other product variable usages -- as selects?
+			if newFlags, subbed := bazel.TryVariableSubstitutions(flags, prop.ProductConfigVariable); subbed {
+				asFlags = append(asFlags, newFlags...)
+			}
+		}
+	}
+	// TODO(b/183595872) warn/error if we're not handling product variables
+
 	for arch, p := range m.GetArchProperties(&BaseCompilerProperties{}) {
 		if cProps, ok := p.(*BaseCompilerProperties); ok {
 			copts.SetValueForArch(arch.Name, cProps.Cflags)
@@ -182,6 +201,7 @@ func ObjectBp2Build(ctx android.TopDownMutatorContext) {
 		Srcs:               android.BazelLabelForModuleSrcExcludes(ctx, srcs, excludeSrcs),
 		Deps:               deps,
 		Copts:              copts,
+		Asflags:            asFlags,
 		Local_include_dirs: localIncludeDirs,
 	}