Don't use libandroid_support post-21.

Test: m checkbuild
Bug: http://b/119587551
Change-Id: I7ee1cdc7c0119dbec0e57522b9b494aeb3c16a43
diff --git a/cc/stl.go b/cc/stl.go
index 8eee612..9dc8107 100644
--- a/cc/stl.go
+++ b/cc/stl.go
@@ -17,6 +17,7 @@
 import (
 	"android/soong/android"
 	"fmt"
+	"strconv"
 )
 
 func getNdkStlFamily(m *Module) string {
@@ -110,6 +111,26 @@
 	}()
 }
 
+func needsLibAndroidSupport(ctx BaseModuleContext) bool {
+	versionStr, err := normalizeNdkApiLevel(ctx, ctx.sdkVersion(), ctx.Arch())
+	if err != nil {
+		ctx.PropertyErrorf("sdk_version", err.Error())
+	}
+
+	if versionStr == "current" {
+		return false
+	}
+
+	version, err := strconv.Atoi(versionStr)
+	if err != nil {
+		panic(fmt.Sprintf(
+			"invalid API level returned from normalizeNdkApiLevel: %q",
+			versionStr))
+	}
+
+	return version < 21
+}
+
 func (stl *stl) deps(ctx BaseModuleContext, deps Deps) Deps {
 	switch stl.Properties.SelectedStl {
 	case "libstdc++":
@@ -141,7 +162,9 @@
 		} else {
 			deps.StaticLibs = append(deps.StaticLibs, stl.Properties.SelectedStl, "ndk_libc++abi")
 		}
-		deps.StaticLibs = append(deps.StaticLibs, "ndk_libandroid_support")
+		if needsLibAndroidSupport(ctx) {
+			deps.StaticLibs = append(deps.StaticLibs, "ndk_libandroid_support")
+		}
 		if ctx.Arch().ArchType == android.Arm {
 			deps.StaticLibs = append(deps.StaticLibs, "ndk_libunwind")
 		}