re PR fortran/31587 (Module files shouldn't be updated if their content doesn't change)

re PR fortran/31587 (Module files shouldn't be updated if their content doesn't change)

	PR fortran/31587

	* lib/gcc-dg.exp (scan-module): New function.
	* gfortran.dg/module_md5_1.f90: New test.

	* module.c (write_char): Add character to the MD5 buffer.
	(read_md5_from_module_file): New function.
	(gfc_dump_module): Compute MD5 for new module file. Call
	read_md5_from_module_file. Only overwrite old module file
	if the new MD5 is different.

From-SVN: r124126