Add default_visibility for soong modules

So that we don't get surprise usages.

Bug: 348717861
Test: m nothing
Change-Id: I47319a727092c1bd936cca88f5713ee977a48b48
diff --git a/cc/config/Android.bp b/cc/config/Android.bp
index 289409f..f514db6 100644
--- a/cc/config/Android.bp
+++ b/cc/config/Android.bp
@@ -35,4 +35,8 @@
     testSrcs: [
         "tidy_test.go",
     ],
+    visibility: [
+        "//build/soong:__subpackages__",
+        "//prebuilts/clang/host/linux-x86/soong",
+    ],
 }