cmake DEAL_II_COMPILER_HAS_DIAGNOSTIC_PRAGMA examples

dealii/dealii cmake/checks/check_02_compiler_features.cmake :318 

CHECK_CXX_SOURCE_COMPILES(
  "
  _Pragma(\"GCC diagnostic push\")
  _Pragma(\"GCC diagnostic ignored \\\\\\\"-Wextra\\\\\\\"\")
  _Pragma(\"GCC diagnostic ignored \\\\\\\"-Wunknown-pragmas\\\\\\\"\")
  _Pragma(\"GCC diagnostic ignored \\\\\\\"-Wpragmas\\\\\\\"\")
  int main() { return 0; }
  _Pragma(\"GCC diagnostic pop\")
  "
  DEAL_II_COMPILER_HAS_DIAGNOSTIC_PRAGMA)