Add a proper check for rustboot

Uncomment log initialization.

Author: marijnh

src/rt/rust.cpp

@@ -80,10 +80,8 @@ extern "C" CDECL int
 rust_start(uintptr_t main_fn, rust_crate const *crate, int argc,
            char **argv, void* crate_map) {
 
-    // FIXME commented out until I figure out how to detect rustboot in a sane
-    // way
-    /* if (NOT_USING_RUSTBOOT)
-          update_log_settings(crate_map, getenv("RUST_LOG"));*/
+    if (crate->abi_tag != ABI_X86_RUSTBOOT_CDECL)
+        update_log_settings(crate_map, getenv("RUST_LOG"));
     rust_srv *srv = new rust_srv();
     rust_kernel *kernel = new rust_kernel(srv);
     kernel->start();