PNG's don't load with allegro5, but BMP's do - c++

Question

I'm trying to learn how to use allegro5 so I installed it from source on their github and it was going fine until I tried to load an image. Here is my code that wasn't working.
#include<allegro5/allegro.h>
#include<allegro5/allegro_image.h>
#include<stdio.h>
int main(int argc, char **argv){
al_init();
al_init_image_addon();
al_create_display(640,560);
ALLEGRO_BITMAP * image = al_load_bitmap("pi.png");
while(true){
al_clear_to_color(al_map_rgb(100,0,0));
if(image == NULL){
printf("Image didn't load properly\n");
return -1;
}
al_draw_bitmap(image, 0, 0, 0);
al_flip_display();
}
}
But after making a pi.bmp in the same directory and then changing the
ALLEGRO_BITMAP * image = al_load_bitmap("pi.png");
to
ALLEGRO_BITMAP * image = al_load_bitmap("pi.bmp");
It works as expected. I already have libpng16-16 and libpng-dev installed. I am compiling the file (main.cpp) with this command:
g++ main.cpp -I/usr/local/include/allegro5 -L/usr/local/lib -lallegro -lallegro_image -lpng
Does anyone know what I am doing wrong?
EDIT: By not working I do mean that image == NULL is true. Also I just tried to do it on my laptop. I believe the problem must be somewhere with my installation. My desktop (the one that doesn't work) is running Ubuntu 18.10 (cosmic) and my laptop is running 18.04 (bionic) and works fine after adding the ppa and updating. It seems they only have pre-compiled binaries for bionic, which is what forced me to compile from source.
EDIT2: #rcorre's answer worked for me! Hopefully this will help someone else out in the future. When building you need to use the command cmake -D WANT_IMAGE_PNG=1 .. from the build directory.