re PR c++/64266 (Can GCC produce local mergeable symbols for *.__FUNCTION__ and ...

re PR c++/64266 (Can GCC produce local mergeable symbols for *.__FUNCTION__ and *.__PRETTY_FUNCTION__ functions?)

	PR c++/64266
	PR c++/70353
	Core issue 1962
	* decl.c (cp_fname_init): Decay the initializer to pointer.
	(cp_make_fname_decl): Set DECL_DECLARED_CONSTEXPR_P,
	DECL_VALUE_EXPR, DECL_INITIALIZED_BY_CONSTANT_EXPRESSION_P.
	Don't call cp_finish_decl.
	* pt.c (tsubst_expr) [DECL_EXPR]: Set DECL_VALUE_EXPR,
	DECL_INITIALIZED_BY_CONSTANT_EXPRESSION_P.  Don't call cp_finish_decl.
	* constexpr.c (cxx_eval_constant_expression) [VAR_DECL]:
	Handle DECL_VALUE_EXPR.

Co-Authored-By: Martin Liska <mliska@suse.cz>
From-SVN: r234484