It was pointed out on gcc-help last night that the -Wplacement-new
warning issues a false positive when a placement new expression is
invoked with an operand that is an element of an array of pointers
(to buffers of unknown size).  The attached patch adjusts
the warning so as to avoid this false positive.

The patch also removes the pointless loop that Jakub questioned
below:

   https://gcc.gnu.org/ml/gcc-patches/2016-04/msg00050.html

Martin