c++: noexcept error recursion [PR100101]

c++: noexcept error recursion [PR100101]

Here instantiating the noexcept-specifier for bar<void>() means
instantiating A<void>::value, which complains about the conversion from 0 to
int* in the default argument of foo.  Since my patch for PR99583, printing
the error context involves looking at C<void>::type, which again wants to
instantiate A<void>::value, which breaks.  For now at least, let's break
this recursion by avoiding looking into the noexcept-specifier in
find_typenames, and limit that to just the uses_parameter_packs case that
PR99583 cares about.

gcc/cp/ChangeLog:

	PR c++/100101
	PR c++/99583
	* pt.c (find_parameter_packs_r) [FUNCTION_TYPE]: Walk into
	TYPE_RAISES_EXCEPTIONS here.
	* tree.c (cp_walk_subtrees): Not here.

gcc/testsuite/ChangeLog:

	PR c++/100101
	* g++.dg/cpp0x/noexcept67.C: New test.