Return `void*` from _d_allocclass so LLVM doesn't do weird things with it... This allows `-instcombine` followed by `-gvn` to do devirtualization, so add `-gvn` in strategic places in the default pass order.

module tangotests.gc2;

import tango.core.Memory;

void main()
{
    char[] tmp = new char[2500];
    GC.collect();
}