rt: Don't log in the stack switching failure path

The runtime is in an uncertain state here and, instead of thinking
about how to make the logger work correctly, let's just avoid it.

Currently, it ends up hitting an assert saying that we can't log on
the rust stack.

Author: brson

src/rt/rust_upcall.cpp

@@ -71,8 +71,8 @@ upcall_call_shim_on_c_stack(void *args, void *fn_ptr) {
     try {
         task->call_on_c_stack(args, fn_ptr);
     } catch (...) {
-        LOG_ERR(task, task, "Native code threw an exception");
-        abort();
+        // Logging here is not reliable
+        assert(false && "Native code threw an exception");
     }
 
     task->record_stack_limit();
@@ -96,9 +96,8 @@ upcall_call_shim_on_rust_stack(void *args, void *fn_ptr) {
     } catch (...) {
         // We can't count on being able to unwind through arbitrary
         // code. Our best option is to just fail hard.
-        LOG_ERR(task, task,
-                "Rust task failed after reentering the Rust stack");
-        abort();
+        // Logging here is not reliable
+        assert(false && "Rust task failed after reentering the Rust stack");
     }
 
     // FIXME: As above