test/fiber/test_queue.rb: Make the stuck test fail.

We observed the 2 tests in the `test/fiber/test_queue.rb` getting stuck
in some GCC compilers in ppc64le Ubuntu, even when the timeout
`queue.pop(timeout: 0.0001)` is set in the code.

This commit is to make the test fail rather than getting stuck.

test/fiber/test_queue.rb

@@ -1,4 +1,5 @@
 # frozen_string_literal: true
+require 'timeout'
 require 'test/unit'
 require_relative 'scheduler'
 
@@ -7,16 +8,18 @@ def test_pop_with_timeout
     queue = Thread::Queue.new
     result = :unspecified
 
-    Thread.new do
-      scheduler = Scheduler.new
-      Fiber.set_scheduler(scheduler)
+    assert_nothing_stuck do
+      Thread.new do
+        scheduler = Scheduler.new
+        Fiber.set_scheduler(scheduler)
 
-      Fiber.schedule do
-        result = queue.pop(timeout: 0.0001)
-      end
+        Fiber.schedule do
+          result = queue.pop(timeout: 0.0001)
+        end
 
-      scheduler.run
-    end.join
+        scheduler.run
+      end.join
+    end
 
     assert_nil result
   end
@@ -26,17 +29,28 @@ def test_pop_with_timeout_and_value
     queue.push(:something)
     result = :unspecified
 
-    Thread.new do
-      scheduler = Scheduler.new
-      Fiber.set_scheduler(scheduler)
+    assert_nothing_stuck do
+      Thread.new do
+        scheduler = Scheduler.new
+        Fiber.set_scheduler(scheduler)
 
-      Fiber.schedule do
-        result = queue.pop(timeout: 0.0001)
-      end
+        Fiber.schedule do
+          result = queue.pop(timeout: 0.0001)
+        end
 
-      scheduler.run
-    end.join
+        scheduler.run
+      end.join
+    end
 
     assert_equal :something, result
   end
+
+  def assert_nothing_stuck(&block)
+    msg = 'The test gets stuck due to a possible compiler bug.'
+    assert_nothing_raised(Timeout::Error, msg) do
+      Timeout::timeout(1) do
+        block.call
+      end
+    end
+  end
 end