PR fortran/21435

	* io.c (compare_to_allowed_values): New function.
	(gfc_match_open): Add checks for constant values of specifiers.
	(gfc_match_close): Add checks for constant values of the STATUS
	specifier.

	* gcc/testsuite/gfortran.dg/io_constraints_3.f90: New test.
	* gcc/testsuite/gfortran.dg/open_access_append_1.f90: Add checks
	for compile-time warnings.
	* gcc/testsuite/gfortran.dg/pr20163-2.f: Likewise.
	* gcc/testsuite/gfortran.dg/iostat_2.f90: Likewise.
	* gcc/testsuite/gfortran.dg/label_4.f90: Delete the temporary
	file.
	* gcc/testsuite/gfortran.dg/direct_io_2.f90: Add a FILE=
	specifier.
	* gcc/testsuite/gfortran.dg/iomsg_1.f90: Add check for
	compile-time warning.

From-SVN: r117685