This specifically fixes unix alloc(): previously when allocation fails
it would (recursively) call alloc() again to create an interface due to
lacking escape analysis.
Also, all other cases shouldn't try to allocate just because something
bad happens at runtime.
TODO: implement escape analysis.
CGo depends on syscall, which (in the standard library) depends on sync,
which depends on the runtime. There are also other import cycles. To be
able to use the syscall package from upstream, stop using CGo.
