Main function not found when running Allegro 5 on OSX

I am trying to get a minimal example of Allegro running on OSX.

I installed the stable version Allegro 5.2 using Homebrew, as specified in the Allegro wiki.

Here is my code (allegro.hpp):

/*
 * This program uses the Allegro game library to display a blank window.
 *
 * It initializes the display and starts up the main game loop. The
 * game loop only checks for two events: timer (determined by the FPS)
 * and display close (when the user tries to close the window).
 *
 * http://www.damienradtke.org/building-a-mario-clone-with-allegro
 */

#include <stdio.h>
#include <allegro5/allegro.h>

constexpr float FPS = 60.0f;

int main(int argc, char** argv) {
  ALLEGRO_DISPLAY *display = NULL;
  ALLEGRO_EVENT_QUEUE *event_queue = NULL;
  ALLEGRO_TIMER *timer = NULL;

  bool running = true;
  bool redraw = true;

  // Initialize allegro
  if (!al_init()) {
    fprintf(stderr, "Failed to initialize allegro.\n");
    return 1;
  }

  // Initialize the timer
  timer = al_create_timer(1.0f / FPS);
  if (!timer) {
    fprintf(stderr, "Failed to create timer.\n");
    return 1;
  }

  // Create the display
  display = al_create_display(640, 480);
  if (!display) {
    fprintf(stderr, "Failed to create display.\n");
    return 1;
  }

  // Create the event queue
  event_queue = al_create_event_queue();
  if (!event_queue) {
    fprintf(stderr, "Failed to create event queue.");
    return 1;
  }

  // Register event sources
  al_register_event_source(event_queue, al_get_display_event_source(display));
  al_register_event_source(event_queue, al_get_timer_event_source(timer));

  // Display a blank screen
  al_clear_to_color(al_map_rgb(100, 149, 237));
  al_flip_display();

  // Start the timer
  al_start_timer(timer);

  // Game loop
  while (running) {
    ALLEGRO_EVENT event;
    ALLEGRO_TIMEOUT timeout;

    // Initialize timeout
    al_init_timeout(&timeout, 0.06);

    // Fetch the event (if one exists)
    bool get_event = al_wait_for_event_until(event_queue, &event, &timeout);

    // Handle the event
    if (get_event) {
      switch (event.type) {
        case ALLEGRO_EVENT_TIMER:
          redraw = true;
          break;
        case ALLEGRO_EVENT_DISPLAY_CLOSE:
          running = false;
          break;
        default:
          fprintf(stderr, "Unsupported event received: %d\n", event.type);
          break;
      }
    }

    // Check if we need to redraw
    if (redraw && al_is_event_queue_empty(event_queue)) {
      // Redraw
      al_clear_to_color(al_map_rgb(100, 149, 237));
      al_flip_display();
      redraw = false;
    }
  } 

  // Clean up
  al_destroy_display(display);
  al_destroy_event_queue(event_queue);

  return 0;
}

Here is my build and execute command:

$ clang++ -I/usr/local/include/ -L/usr/local/lib -lallegro -lallegro_main allegro.hpp -std=c++14 && ./a.out

And here is the error I recieve:

dyld: Symbol not found: __al_mangled_main
  Referenced from: /usr/local/opt/allegro/lib/liballegro_main.5.2.dylib
  Expected in: flat namespace
 in /usr/local/opt/allegro/lib/liballegro_main.5.2.dylib
Trace/BPT trap: 5

I have already tried the solution given elsewhere:

1. Change the main-function's signature to int main(int argc, char** argv)
2. Link liballegro_main.dylib

You named it allegro.hpp, even though it is a source file, not a header file.

Rename it to something.cpp or something.cc.