re PR c++/5998 (regression, all builtins disabled)

re PR c++/5998 (regression, all builtins disabled)

	* include/c_std/std_cmath.h:  To prevent problems overloading
	g++ builtins, use the double variants from the global namespace
	before defining float and long double variants in std::.

	PR c++/5998:
	* decl.c (cxx_init_decl_processing): Re-enable built-in functions
	in the g++ front-end.
	(duplicate_decl): Allow redefinition of anticipated built-ins.
	Fix inlining problem by over-writing the old DECL_RTL.
	(lookup_namespace_name): Fail to find an identifier in the
	specified namespace if its still anticipated.
	(builtin_function_1): New function split out from builtin_function
	to create a builtin in the current namespace with given context.
	(builtin_function): Call builtin_function_1 to define the
	appropriate builtins in both the std and global namespaces.
	(select_decl): Don't test for anticipated decls here.
	(unqualified_namespace_lookup): Instead ignore them whilst
	searching through scopes and namespaces.
	* decl2.c (do_nonmember_using_decl): If a using declaration
	specifies an anticipated built-in function, mark it as no longer
	anticipated in that scope.
	(ambiguous_decl):  Avoid resolving to an anticipated decl.
	* lex.c (do_scoped_id): Fail to find an identifier in the global
	namespace if its still anticipated.

	* g++.old-deja/g++.other/builtins5.C: New test.
	* g++.old-deja/g++.other/builtins6.C: New test.
	* g++.old-deja/g++.other/builtins7.C: New test.
	* g++.old-deja/g++.other/builtins8.C: New test.
	* g++.old-deja/g++.other/builtins9.C: New test.

From-SVN: r51568