Revert non-NFC change

As it's essentially a bug fix.

Author: kleisauke

system/lib/libc/musl/src/thread/pthread_barrier_wait.c

@@ -93,10 +93,10 @@ int pthread_barrier_wait(pthread_barrier_t *b)
 			if (is_runtime_thread) {
 				int e;
 				do {
-					// Assist other threads by executing proxied operations that are effectively singlethreaded.
-					emscripten_main_thread_process_queued_calls();
 					// Main runtime thread may need to run proxied calls, so sleep in very small slices to be responsive.
 					e = emscripten_futex_wait(&inst->finished, 1, 1);
+					// Assist other threads by executing proxied operations that are effectively singlethreaded.
+					emscripten_main_thread_process_queued_calls();
 				} while (e == -ETIMEDOUT);
 			} else {
 				// Can wait in one go.