re PR fortran/31629 (option to make module entities PRIVATE by default)

re PR fortran/31629 (option to make module entities PRIVATE by default)

	PR fortran/31629

	* lang.opt (-fmodule-private): New option.
	* gfortran.h (gfc_option_t): Add flag_module_private member.
	* invoke.texi (-fmodule-private): Document the new option.
	* module.c (gfc_check_access): Allow the -fmodule-private option
	to modify the default behaviour.
	* options.c (gfc_init_options): Initialize flag_module_private.
	(gfc_handle_option): Handle -fmodule-private.

	* gfortran.dg/module_private_1.f90: New test.

From-SVN: r127381