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 internal.mem;

extern(C):

void* realloc(void*,size_t);
void free(void*);

void* _d_realloc(void* ptr, size_t n)
{
    return realloc(ptr, n);
}

void _d_free(void* ptr)
{
    free(ptr);
}