c++: uninstantiated template friends

[Nathan Sidwell]

template friends need to be recognized by module streaming and
associated with the befriending class.	but their context is that of
the friend (a namespace or other class).  This adds a flag to mark
such templates,	and uses their DECL_CHAIN to point at the befriender.

	gcc/cp
         * cp-tree.h (DECL_UNINSTANTIATED_TEMPLATE_FRIEND): New.
	* pt.c (push_template_decl): Set it.
         (tsubst_friend_function): Clear	it.

pushing to trunk

-- 
Nathan Sidwell
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