cmake DEAL_II_COMPILER_HAS_RESTRICT_KEYWORD examples

dealii/dealii cmake/checks/check_02_compiler_features.cmake :294 

CHECK_CXX_SOURCE_COMPILES(
  "
          void fn (double *__restrict a, double *__restrict b) { a[0] = b[0]; a[1] = b[0]; }
          int main() { }
  "
  DEAL_II_COMPILER_HAS_RESTRICT_KEYWORD
  )