Move build -> gn/standalone

Make it explicit that those gn files are only for the standalone
build.

Bug: 68710794
Change-Id: I7e2a15219d63b62bf8f249becfdbf39fda2cc183
diff --git a/gn/BUILD.gn b/gn/BUILD.gn
index 92fba54..41b5217 100644
--- a/gn/BUILD.gn
+++ b/gn/BUILD.gn
@@ -83,8 +83,8 @@
   public_configs = [ ":default_config" ]
   if (!build_with_chromium) {
     public_deps = [
-      "//build/libc++:deps",
-      "//build/sanitizers:deps",
+      "//gn/standalone/libc++:deps",
+      "//gn/standalone/sanitizers:deps",
     ]
   }
 }