androidmk: add support for ifdef USE_MINGW

Change-Id: Ib3436cb4fd2469f5be2f7ee1525709eb1e143dbf

androidmk/cmd/androidmk/android.go

@@ -102,6 +102,7 @@ var conditionalTranslations = map[string]struct {
 	"($(BUILD_OS), darwin)": {"target", "darwin"},
 	"($(BUILD_OS),linux)":   {"target", "linux"},
 	"($(BUILD_OS), linux)":  {"target", "linux"},
+	"USE_MINGW":             {"target", "windows"},
 }
 
 func mydir(args []string) string {

androidmk/cmd/androidmk/androidmk.go

@@ -117,9 +117,9 @@ func main() {
 					file.errorf(directive, "unsupported include")
 					continue
 				}
-			case "ifeq", "ifneq":
+			case "ifeq", "ifneq", "ifdef", "ifndef":
 				args := directive.Args.Dump()
-				eq := directive.Name == "ifeq"
+				eq := directive.Name == "ifeq" || directive.Name == "ifdef"
 				if _, ok := conditionalTranslations[args]; ok {
 					newCond := conditional{args, eq}
 					conds = append(conds, &newCond)