c: use CONST_DECL for enumerators in TYPE_VALUES

c: use CONST_DECL for enumerators in TYPE_VALUES

The C and C++ FEs differ in TYPE_VALUES for an enum type: an entry in
the list in the C++ FE has a CONST_DECL in the TREE_VALUE, but the C FE
has only the numerical value of the CONST_DECL there.  This has caused
me some trouble in my PR105497 patch.  Using a CONST_DECL is preferable
because a CONST_DECL can track more information (e.g., attributes), and
you can always get the value simply by looking at its DECL_INITIAL.

This turned out to be a trivial change.  One place in godump.cc had to be
adjusted.  I'm not changing the CONST_DECL check in c_do_switch_warnings
because I'll be changing it soon in my next patch.  I didn't see any other
checks that this patch makes redundant.

gcc/c/ChangeLog:

	* c-decl.cc (finish_enum): Store the CONST_DECL into TREE_VALUE, not
	its value.

gcc/ChangeLog:

	* godump.cc (go_output_typedef): Use the DECL_INITIAL of the TREE_VALUE.