c++: Friend classes don't shadow enclosing template class paramater [PR118255]

c++: Friend classes don't shadow enclosing template class paramater [PR118255]

We currently reject the following code

=== code here ===
template <int non_template> struct S { friend class non_template; };
class non_template {};
S<0> s;
=== code here ===

While EDG agrees with the current behaviour, clang and MSVC don't (see
https://godbolt.org/z/69TGaabhd), and I believe that this code is valid,
since the friend clause does not actually declare a type, so it cannot
shadow anything. The fact that we didn't error out if the non_template
class was declared before S backs this up as well.

This patch fixes this by skipping the call to check_template_shadow for
hidden bindings.

	PR c++/118255

gcc/cp/ChangeLog:

	* name-lookup.cc (pushdecl): Don't call check_template_shadow
	for hidden bindings.

gcc/testsuite/ChangeLog:

	* g++.dg/lookup/pr99116-1.C: Adjust test expectation.
	* g++.dg/template/friend84.C: New test.