drm_hwcomposer: Set std=c++17 in Android.bp

The CI is configured to build using std=c++17, so update the default
build flags to the same.

This avoids the case where a contributor's change builds properly
locally, but fails in CI due to the usage of c++20 features.

Change-Id: I41d3115a314305e3863cd65623b244e9ab82dc3c
Signed-off-by: Drew Davenport <ddavenport@google.com>

Android.bp

@@ -55,6 +55,8 @@ cc_defaults {
         "-DHWC2_USE_CPP11",
     ],
 
+    cpp_std: "gnu++17",
+
     relative_install_path: "hw",
     vendor: true,
 }