GN: Fix compile errors with os==chromeos mojo/public build

mojo/public/BUILD.gn

Index: mojo/public/BUILD.gn
diff --git a/mojo/public/BUILD.gn b/mojo/public/BUILD.gn
index 03aefb95e740eb544dc2afa51930d2dd7b271efa..1bd12b0e1811ed70718768b440abcfe3bb5c8a07 100644
--- a/mojo/public/BUILD.gn
+++ b/mojo/public/BUILD.gn
@@ -3,15 +3,12 @@
 # found in the LICENSE file.
 
 group("public") {
+  # Meta-target, don't link into production code.
+  testonly = true
   deps = [
-    "//mojo/public/c/system",
-    "//mojo/public/cpp/application:standalone",
-    "//mojo/public/cpp/bindings",
-    "//mojo/public/cpp/environment:standalone",
-    "//mojo/public/cpp/utility",
+    ":libmojo_sdk",
+    ":sdk",
     "//mojo/public/interfaces/bindings/tests:test_interfaces",
-    "//mojo/public/interfaces/application",
-    "//mojo/public/js/bindings",
   ]
 
   if (is_linux) {
@@ -27,3 +24,20 @@ group("public") {
     ]
   }
 }
+
+group("sdk") {
+  deps = [
+    "//mojo/public/c/system",
+    "//mojo/public/cpp/application:standalone",
+    "//mojo/public/cpp/bindings",
+    "//mojo/public/cpp/environment:standalone",
+    "//mojo/public/cpp/utility",
+    "//mojo/public/interfaces/application",
+    "//mojo/public/js/bindings",
+  ]
+}
+
+static_library("libmojo_sdk") {
+  complete_static_lib = true
+  deps = [ ":sdk" ]
+}