trusty: Add libtrusty_test

Used by tests on the system side of the Treble boundary, e.g. fuzzing

Test: m libtrusty libtrusty_test
Change-Id: I56a15c80eb7c4b9e51f8e59a7cd1abdfc35d8d5a

trusty/libtrusty/Android.bp

@@ -12,10 +12,8 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-cc_library {
-    name: "libtrusty",
-    vendor: true,
-
+cc_defaults {
+    name: "libtrusty_defaults",
     srcs: ["trusty.c"],
     export_include_dirs: ["include"],
     cflags: [
@@ -25,3 +23,16 @@ cc_library {
 
     shared_libs: ["liblog"],
 }
+
+cc_library {
+    name: "libtrusty",
+    vendor: true,
+    defaults: ["libtrusty_defaults"],
+}
+
+// TODO(b/170753563): cc_fuzz can't deal with vendor components. Build libtrusty
+// for system.
+cc_test_library {
+    name: "libtrusty_test",
+    defaults: ["libtrusty_defaults"],
+}