Simplify types of TYPE_VALUES in enumeral types

Simplify types of TYPE_VALUES in enumeral types

streaming code assumes that INTEGER_CST never appears in non-trivial component.
This is not true and we sometimes stream such components which sort of silently
works but breaks our IL invariant about tree sharing.  This patch fixes one
instance of this problem where ENUMERAL_TYPE lists all its valids in TYPE_VALUES
that with some FEs (like Ada and C++) are having the enumeral type as a type
while in other FEs (like C) are simple integer types.

I convert them all to integers which also increases chance that they will be
shared with other integer constants at stream time.

gcc/

	* tree.c (free_lang_data_in_type): Simpify types of TYPE_VALUES in
	enumeral types.