Support aidl cpp generation

Ideally we'd calculate the headers that are written here too, but I'll
add that in a later change that actually enforces the generated header
list.

Test: mmma -j system/tools/aidl
Change-Id: Ifd2e8e8ff444b0f67270fb5156e7bf7bceddb6be

cc/util.go

@@ -94,6 +94,7 @@ func flagsToBuilderFlags(in Flags) builderFlags {
 		cppFlags:    strings.Join(in.CppFlags, " "),
 		yaccFlags:   strings.Join(in.YaccFlags, " "),
 		protoFlags:  strings.Join(in.protoFlags, " "),
+		aidlFlags:   strings.Join(in.aidlFlags, " "),
 		ldFlags:     strings.Join(in.LdFlags, " "),
 		libFlags:    strings.Join(in.libFlags, " "),
 		tidyFlags:   strings.Join(in.TidyFlags, " "),