vndk/window.h must be C compatible

Test: added a c compatibility test
Bug: 36725813
Change-Id: Ic7e1c8b50e1818707a9a457d84ed74e7e6c816c8
diff --git a/libs/nativewindow/tests/Android.bp b/libs/nativewindow/tests/Android.bp
index 437ab75..6d78770 100644
--- a/libs/nativewindow/tests/Android.bp
+++ b/libs/nativewindow/tests/Android.bp
@@ -17,5 +17,7 @@
 cc_test {
     name: "AHardwareBufferTest",
     shared_libs: ["libnativewindow"],
-    srcs: ["AHardwareBufferTest.cpp"],
+    srcs: [
+        "AHardwareBufferTest.cpp",
+        "c_compatibility.c"],
 }