Replace soong variables with cc_defaults.

Bug: 64318482
Test: links
Change-Id: Id03af485a4282db5b9a13a79fce00a2d66b59ffc
diff --git a/Android.bp b/Android.bp
index ae04548..6abdab8 100644
--- a/Android.bp
+++ b/Android.bp
@@ -18,13 +18,17 @@
     "transport",      // libhidltransport
 ]
 
-libhidl_flags = [
-    "-Wall",
-    "-Werror",
-]
+cc_defaults {
+    name: "libhidl-defaults",
+    cflags: [
+        "-Wall",
+        "-Werror",
+    ],
+}
 
 cc_test {
     name: "libhidl_test",
+    defaults: ["libhidl-defaults"],
     gtest: false,
     srcs: ["test_main.cpp"],
 
@@ -42,5 +46,5 @@
     cflags: [
         "-O0",
         "-g",
-    ] + libhidl_flags,
+    ],
 }