cmake: add khronos include directories with PRIVATE visibility

test/CMakeLists.txt

@@ -131,6 +131,7 @@ macro(add_sdl_test_executable TARGET)
         add_executable(${TARGET} ${AST_SOURCES} ${EXTRA_SOURCES})
     endif()
     SDL_AddCommonCompilerFlags(${TARGET})
+    target_include_directories(${TARGET} PRIVATE "${SDL3_SOURCE_DIR}/src/video/khronos")
     target_link_libraries(${TARGET} PRIVATE SDL3::SDL3_test SDL3::${sdl_name_component})
     if(NOT AST_NO_C90 AND NOT SDL_CMAKE_PLATFORM MATCHES "^(n3ds|ps2|psp)$")
         set_property(TARGET ${TARGET} PROPERTY C_STANDARD 90)