Reduce flakiness in top_test

Turns out clang was being clever and optimizing away an entire if
clause.

Still a bit flaky, but it is much better now...

Signed-off-by: James Kuszmaul <james.kuszmaul@bluerivertech.com>
Change-Id: I75f790fa2be60fd00dd84376185b1aa22c5a4b62
diff --git a/aos/util/top_test.cc b/aos/util/top_test.cc
index cf7e03e..36afd64 100644
--- a/aos/util/top_test.cc
+++ b/aos/util/top_test.cc
@@ -92,9 +92,16 @@
     const pid_t pid = fork();
     PCHECK(pid >= 0);
     if (pid == 0) {
+      LOG(INFO) << "In child process.";
       while (true) {
+        // This is a "please don't optimize me out" thing for the compiler.
+        // Otherwise, the entire if (pid == 0) block can get optimized away...
+        asm("");
+        continue;
       }
+      LOG(FATAL) << "This should be unreachable.";
     } else {
+      CHECK_NE(0, pid) << "The compiler is messing with you.";
       children.push_back(pid);
     }
   }