std::allocator::deallocate support sized-deallocation

std::allocator::deallocate support sized-deallocation

Pass the size to the allocator so that it may optimize deallocation.
This was seen to significantly reduce the work required in jemalloc,
with about 40% reduction in CPU cycles in the free path.

Note jemalloc >= 5.2 is required to fix a crash with 0 sizes.

2019-05-20  Pádraig Brady  <pbrady@fb.com>

	* libstdc++-v3/include/ext/new_allocator.h (deallocate): Pass the size
	to the deallocator with -fsized-deallocation.

From-SVN: r271409