`std.experimental.allocator.make` doesn't even try to respect class alignment

[ichordev]

The following code triggers an assert in core.lifetime.emplace due to the allocated pointer for S not being aligned to __traits(classInstanceAlignment, S):

class S{}

void main(){
	import std.experimental.allocator: make;
	import std.experimental.allocator.building_blocks: BitmappedBlock;
	auto alloc = BitmappedBlock!(17,1)(new ubyte[](64));
	auto a = make!S(alloc);
	auto b = make!S(alloc); //core.exception.AssertError@/dlang/ldc-1.41.0/bin/../import/core/lifetime.d(207): chunk is not aligned.
}

BitmappedBlock implements alignedAllocate, which make could use to trivially avoid this issue.