anbox: Make android-emugl compile with C++14.

This is suggested in https://github.com/anbox/anbox/issues/2119 to support newer versions of gtest.

pkgs/os-specific/linux/anbox/0002-NixOS-Build-android-emugl-with-cpp-14.patch

@@ -0,0 +1,11 @@
+--- a/external/android-emugl/CMakeLists.txt
++++ b/external/android-emugl/CMakeLists.txt
+@@ -1,7 +1,7 @@
+ # Don't treat any warnings as error as we take the source directly from
+ # upstream and just compile it.
+ set(CMAKE_C_FLAGS "-Wall")
+-set(CMAKE_CXX_FLAGS "-std=c++11 -Wall")
++set(CMAKE_CXX_FLAGS "-std=c++14 -Wall")
+ 
+ # Ensure -fPIC
+ set(CMAKE_POSITION_INDEPENDENT_CODE ON)

pkgs/os-specific/linux/anbox/default.nix

@@ -130,6 +130,8 @@ stdenv.mkDerivation rec {
     })
     # Ensures generated desktop files work on store path change
     ./0001-NixOS-Use-anbox-from-PATH-in-desktop-files.patch
+    # Allows android-emugl to build with gtest 1.13+
+    ./0002-NixOS-Build-android-emugl-with-cpp-14.patch
     # Provide window icons
     (fetchpatch {
       url = "https://github.com/samueldr/anbox/commit/2387f4fcffc0e19e52e58fb6f8264fbe87aafe4d.patch";