c++: lambdas with internal linkage are different to no-linkage [PR94426]

c++: lambdas with internal linkage are different to no-linkage [PR94426]

My fix for 94147 was confusing no-linkage with internal linkage, at
the language level.  That's wrong. (the std is confusing here, because
it describes linkage of names (which is wrong), and lambdas have no
names)

Lambdas with extra-scope, have linkage.  However, at the
implementation-level that linkage is at least as restricted as the
linkage of the extra-scope decl.

Further, when instantiating a variable initialized by a lambda, we
must determine the visibility of the variable itself, before
instantiating its initializer.  If the template arguments are internal
(or no-linkage), the variable will have internal linkage, regardless
of the linkage of the template it is instantiated from.  We need to
know that before instantiating the lambda, so we can restrict its
linkage correctly.

	* decl2.c (determine_visibility): A lambda's visibility is
	affected by its extra scope.
	* pt.c (instantiate_decl): Determine var's visibility before
	instantiating its initializer.
	* tree.c (no_linkage_check): Revert code looking at visibility of
	lambda's extra scope.
`	gcc/cp/
	* g++.dg/cpp0x/lambda/pr94426-[12].C: New.
	* g++.dg/abi/lambda-vis.C: Drop a warning.
	* g++.dg/cpp0x/lambda/lambda-mangle.C: Lambda visibility on
	variable changes.
	* g++.dg/opt/dump1.C: Drop warnings of no import.