Give glad a CMake file

Today I learned that CMake will error if the project shares a
dependency with a nested CMake file (which could be from an
entirely-separate project that you have no control over).

I'm starting to really hate CMake.

CMakeLists.txt

@@ -526,7 +526,8 @@ else()
 endif()
 
 if(BACKEND_RENDERER MATCHES "OpenGL3")
-	target_sources(CSE2 PRIVATE "external/glad/src/glad.c" "external/glad/include/glad/glad.h" "external/glad/include/KHR/khrplatform.h")
+	add_subdirectory("external/glad" EXCLUDE_FROM_ALL)
+	target_link_libraries(CSE2 PRIVATE glad)
 
 	find_package(OpenGL REQUIRED)
 	target_link_libraries(CSE2 PRIVATE OpenGL::GL ${CMAKE_DL_LIBS})

DoConfig/CMakeLists.txt

@@ -9,9 +9,6 @@ project(DoConfig LANGUAGES C CXX)
 
 add_executable(DoConfig WIN32
 	"icon.rc"
-	"../external/glad/include/glad/glad.h"
-	"../external/glad/include/KHR/khrplatform.h"
-	"../external/glad/src/glad.c"
 	"DoConfig.cpp"
 	"imgui/imconfig.h"
 	"imgui/imgui.cpp"
@@ -71,6 +68,16 @@ endif()
 # Dependencies #
 ################
 
+# glad
+
+if(NOT TARGET glad)
+	add_subdirectory("../external/glad" "glad" EXCLUDE_FROM_ALL)
+endif()
+
+target_link_libraries(DoConfig PRIVATE glad)
+
+# GLFW3
+
 if(NOT FORCE_LOCAL_LIBS)
 	find_package(PkgConfig QUIET)
 endif()

external/glad/CMakeLists.txt

@@ -0,0 +1,11 @@
+cmake_minimum_required(VERSION 3.12)
+
+project(glad LANGUAGES C)
+
+add_library(glad
+	"include/glad/glad.h"
+	"include/KHR/khrplatform.h"
+	"src/glad.c"
+)
+
+target_include_directories(glad PUBLIC "include")

external/glad/include/glad/glad.h

@@ -86,7 +86,7 @@ GLAPI int gladLoadGL(void);
 
 GLAPI int gladLoadGLLoader(GLADloadproc);
 
-#include "../KHR/khrplatform.h"
+#include <KHR/khrplatform.h>
 typedef unsigned int GLenum;
 typedef unsigned char GLboolean;
 typedef unsigned int GLbitfield;

external/glad/src/glad.c

@@ -22,7 +22,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
-#include "../include/glad/glad.h"
+#include <glad/glad.h>
 
 static void* get_proc(const char *namez);
 

src/Backends/Rendering/OpenGL3.cpp

@@ -10,7 +10,7 @@
 #ifdef USE_OPENGLES2
 #include <GLES2/gl2.h>
 #else
-#include "../../../external/glad/include/glad/glad.h"
+#include <glad/glad.h>
 #endif
 
 #define SPRITEBATCH_IMPLEMENTATION