cmake HAS_C11_THREADS examples

KhronosGroup/OpenCL-SDK samples/core/callback/CMakeLists.txt :29

try_compile(
    HAS_C11_THREADS
    "${CMAKE_CURRENT_BINARY_DIR}"
    SOURCES "${CMAKE_CURRENT_BINARY_DIR}/threads.c"
    C_STANDARD 11
    C_STANDARD_REQUIRED ON
)