PR fortran/95090 - ICE: identifier overflow

PR fortran/95090 - ICE: identifier overflow

The initial fix for this PR uncovered several latent issues with further
too small string buffers which showed up only when testing on i686.
Provide sufficiently large temporaries.

2020-05-29  Harald Anlauf  <anlauf@gmx.de>

gcc/fortran/
	PR fortran/95090
	* class.c (get_unique_type_string): Enlarge temporary for
	name-mangling.  Use strncpy to prevent buffer overrun.
	(get_unique_hashed_string): Enlarge temporary.
	(gfc_hash_value): Enlarge temporary for name-mangling.