Don't call static desructors when Fatal() errors occur (#1722)

This was causing a deadlock while destroying the thread pool.

Author: sbc100

src/support/threads.cpp

@@ -128,7 +128,7 @@ void ThreadPool::initialize(size_t num) {
 }
 
 size_t ThreadPool::getNumCores() {
-#if EMSCRIPTEN
+#ifdef __EMSCRIPTEN__
   return 1;
 #else
   size_t num = std::max(1U, std::thread::hardware_concurrency());
@@ -181,7 +181,7 @@ void ThreadPool::work(std::vector<std::function<ThreadWorkState ()>>& doWorkers)
   }
   DEBUG_POOL("main thread waiting\n");
   condition.wait(lock, [this]() { return areThreadsReady(); });
-  DEBUG_POOL("main thread waiting\n");
+  DEBUG_POOL("main thread done waiting\n");
   DEBUG_POOL("running = false\n");
   running = false;
   DEBUG_POOL("work() is done\n");

src/support/utilities.h

@@ -71,7 +71,10 @@ class Fatal {
   }
   WASM_NORETURN ~Fatal() {
     std::cerr << "\n";
-    exit(1);
+    // Use _Exit here to avoid calling static destructors. This avoids deadlocks
+    // in (for example) the thread worker pool, where workers hold a lock while
+    // performing their work.
+    _Exit(1);
   }
 };