Move NDK test modules into cc/testing.go

Move the NDK modules defined in app_test.go into cc/testing.go in
preparation for using sdk_version: "current" in more tests.

Test: all soong tests
Change-Id: I80bc31225fb4562fce42781219cefbbd6affae06
diff --git a/rust/rust_test.go b/rust/rust_test.go
index afe530a..020581d 100644
--- a/rust/rust_test.go
+++ b/rust/rust_test.go
@@ -22,6 +22,7 @@
 	"testing"
 
 	"android/soong/android"
+	"android/soong/cc"
 )
 
 var (
@@ -61,6 +62,8 @@
 		"libz.so":    nil,
 	}
 
+	cc.GatherRequiredFilesForTest(fs)
+
 	return android.TestArchConfig(buildDir, nil, bp, fs)
 }