Update foregoing patches to leave rust_crate alone.

Apparently it can't live in the main binary, since on non-Linux
platforms, dynamics libs won't find symbols in the binary. This
removes the crate_map pointer from rust_crate again, and instead
passes it as an extra argument to rust_start. Rustboot doesn't pass
this argument, but supposedly that's okay as long as we don't actually
use it on that platform.

src/rt/rust.cpp

@@ -78,9 +78,11 @@ command_line_args : public dom_owned<command_line_args>
 
 extern "C" CDECL int
 rust_start(uintptr_t main_fn, rust_crate const *crate, int argc,
-           char **argv) {
+           char **argv, void* crate_map) {
 
-    crate->update_log_settings(getenv("RUST_LOG"));
+    // Only when we're on rustc is the last argument passed
+    if (!crate->get_image_base())
+        update_log_settings(crate_map, getenv("RUST_LOG"));
     rust_srv *srv = new rust_srv();
     rust_kernel *kernel = new rust_kernel(srv);
     kernel->start();