Undefined reference to 'glfw...' functions when trying to compile from object files

Question

I'm trying to learn OpenGL and was able to compile my project if I compile them directly from the source code. (EDIT: Very important that I only started having problems once I started to use object files.)

However, recently the compile time has been a little too long so I wrote a makefile that compiles object files first and only update them if needed. For some reason, I can't link the object files and returns the following error:

Compiling executable -> ./bin/2D_GAME
g++ -std=c++11 -Wall -Wextra -lglfw3 -lGL -lXrandr -lXinerama -lXcursor -lXi -lXxf86vm -lX11 -lpthread -lrt -lm -ldl -o 2D_GAME obj/main.o obj/game.o obj/stb_image.o obj/graphics/texture/texture_manager.o obj/graphics/texture/texture_2D.o obj/graphics/system/renderer/2D_Map/renderer_map.o obj/graphics/system/sprite/sprite_loader.o obj/graphics/glad/glad.o obj/graphics/shader/shader.o obj/utils.o
/usr/bin/ld: obj/main.o: in function `processInput':
main.cpp:(.text+0x19): undefined reference to `glfwGetKey'
/usr/bin/ld: main.cpp:(.text+0x34): undefined reference to `glfwSetWindowShouldClose'
/usr/bin/ld: obj/main.o: in function `main':
main.cpp:(.text+0x66): undefined reference to `glfwInit'
/usr/bin/ld: main.cpp:(.text+0x75): undefined reference to `glfwWindowHint'
/usr/bin/ld: main.cpp:(.text+0x84): undefined reference to `glfwWindowHint'
/usr/bin/ld: main.cpp:(.text+0x93): undefined reference to `glfwWindowHint'
/usr/bin/ld: main.cpp:(.text+0xb4): undefined reference to `glfwCreateWindow'
/usr/bin/ld: main.cpp:(.text+0xf2): undefined reference to `glfwTerminate'
/usr/bin/ld: main.cpp:(.text+0x10b): undefined reference to `glfwMakeContextCurrent'
/usr/bin/ld: main.cpp:(.text+0x112): undefined reference to `glfwGetProcAddress'
/usr/bin/ld: main.cpp:(.text+0x188): undefined reference to `glfwSetFramebufferSizeCallback'
/usr/bin/ld: main.cpp:(.text+0x274): undefined reference to `glfwWindowShouldClose'
/usr/bin/ld: main.cpp:(.text+0x75c): undefined reference to `glfwSwapBuffers'
/usr/bin/ld: main.cpp:(.text+0x761): undefined reference to `glfwPollEvents'
/usr/bin/ld: main.cpp:(.text+0x76b): undefined reference to `glfwTerminate'
collect2: error: ld returned 1 exit status
make: *** [makefile:31: 2D_GAME] Error 1

Somehow, its all related to OpenGL but I can't figure out why. The last time I got this kind of error was because I forgot to tell the compiler what static libraries to use. But this time that doesn't seem to be the case.

Any help would be greatly appreciated!

Just in case, here is what is in main.cpp main.cpp:

#include <iostream>
extern "C" {
#include <glad/glad.h>
#include <GLFW/glfw3.h>
}
#include "shader.h"
#include "stb_image.h"
#include "texture_2D.h"
#include "sprite_loader.h"
#include <glm/glm.hpp>
#include <glm/gtc/matrix_transform.hpp>
#include <glm/gtc/type_ptr.hpp>

// window resize callback function
void
framebuffer_size_callback(GLFWwindow * window, int width, int height);

// user input test: Pressing ESC key will close the window
void
processInput(GLFWwindow * window)
{
    if (glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS)
        glfwSetWindowShouldClose(window, true);
}

int
main(int argc, char ** argv)
{
    // Initialize glfw
    glfwInit();
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

    GLFWwindow * window = glfwCreateWindow(800, 600, "2D_RPG", NULL, NULL);
    if (window == NULL) {
        std::cout << "Failed to create GLFW window." << std::endl;
        glfwTerminate();
        return 1;
    }
    glfwMakeContextCurrent(window);

    // Initialize GLAD
    if (!gladLoadGLLoader((GLADloadproc) glfwGetProcAddress)) {
        std::cout << "Failed to initialize GLAD." << std::endl;
        return 1;
    }
    glViewport(0, 0, 800, 600);
    glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);

    Shader shader("./resources/shaders/vertex/test1.vs", "./resources/shaders/fragment/test1.fs");

    Texture2D texture;
    texture.generate("./resources/sprites/test/test0.jpg");

    Sprite_Loader sprite_loader(shader);

    shader.use();
    glm::mat4 projection = glm::ortho(0.0f, static_cast<GLfloat>(800), static_cast<GLfloat>(600), 0.0f, -1.0f, 1.0f);
    glUniformMatrix4fv(glGetUniformLocation(shader.ID, "projection"), 1, GL_FALSE, glm::value_ptr(projection));

    // render loop
    while (!glfwWindowShouldClose(window)) {
        // input
        processInput(window);

        // render code
        glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT);

        sprite_loader.draw(texture, glm::vec2(0, 0), glm::vec2(100, 100), 1.57f, glm::vec3(0.0f, 0.0f, 1.0f));
        sprite_loader.draw(texture, glm::vec2(100, 0), glm::vec2(100, 100), 1.57f, glm::vec3(0.0f, 1.0f, 0.0f));
        sprite_loader.draw(texture, glm::vec2(0, 100), glm::vec2(100, 100), 1.57f, glm::vec3(1.0f, 0.0f, 0.0f));
        sprite_loader.draw(texture, glm::vec2(100, 100), glm::vec2(300, 300), 0.0f, glm::vec3(1.0f, 1.0f, 1.0f));
        sprite_loader.draw(texture, glm::vec2(200, 0), glm::vec2(200, 100), 0.0f, glm::vec3(1.0f, 1.0f, 1.0f));
        sprite_loader.draw(texture, glm::vec2(0, 200), glm::vec2(100, 200), 0.0f, glm::vec3(1.0f, 1.0f, 1.0f));

        // check all events and swap buffers
        glfwSwapBuffers(window);
        glfwPollEvents();
    }

    glfwTerminate();

    return 0;
} // main

void
framebuffer_size_callback(GLFWwindow * window, int width, int height)
{
    glViewport(0, 0, width, height);
}

EDIT: Prior to asking this question, I thought this was because of C++ linkage but that doesn't seem to fix the problem.