re PR tree-optimization/37345 (Segfault in decl_function_context (TYPE_MAIN_VARIANT))

	PR tree-optimization/37345
	PR tree-optimization/37358
	PR tree-optimization/37357
	* tree.c (build_function_type_skip_args): Build distinct type copy;
	set TYPE_CONTEXT.
	(build_function_decl_skip_args): Set type of new decl not orig decl;
	clear DECL_VINDEX for methods turned into functions.

From-SVN: r139980