c++: Fix sizeof VLA lambda capture.

c++: Fix sizeof VLA lambda capture.

sizeof a VLA type is not a constant in C or the GNU C++ extension, so we
need to capture the VLA even in unevaluated context.  For PR60855 we stopped
looking through a previous capture, but we also need to capture the first
time the variable is mentioned.

	PR c++/86216
	* semantics.c (process_outer_var_ref): Capture VLAs even in
	unevaluated context.