message: Add configure option for c++17
diff: @@ -66,8 +66,20 @@ case $host in
  lt_cv_deplibs_check_method="pass_all"
  ;;
  esac
  -dnl Require C++11 compiler (no GNU extensions)
  +
  +AC_ARG_ENABLE([c++17],
  + [AS_HELP_STRING([--enable-c++17],
  + [enable compilation in c++17 mode (disabled by default)])],
  + [use_cxx17=$enableval],
  + [use_cxx17=no])
  +
  +dnl Require C++11 or C++17 compiler (no GNU extensions)
  +if test "x$use_cxx17" = xyes; then
  + AX_CXX_COMPILE_STDCXX([17], [noext], [mandatory])
  +else
  AX_CXX_COMPILE_STDCXX([11], [noext], [mandatory])
  +fi
  +
  dnl Check if -latomic is required for <std::atomic>
  CHECK_ATOMIC
  