Declare variables extern in headers

Fixes linkage errors on GCC 10

src/engine/logger.h

@@ -8,7 +8,7 @@ typedef enum {
 	LOGLEVEL_DEBUG
 } LogLevel;
 
-LogLevel logLevel;
+extern LogLevel logLevel;
 
 #define logError(...) logMessage(LOGLEVEL_ERROR, __func__, __VA_ARGS__)
 #define logWarning(...) logMessage(LOGLEVEL_WARNING, __func__, __VA_ARGS__)

src/engine/render.h

@@ -3,8 +3,8 @@
 
 #include "scene.h"
 
-float viewportAspectRatio;
-const Scene* cameraAnchor;
+extern float viewportAspectRatio;
+extern const Scene* cameraAnchor;
 
 void initRender();
 void renderFrame();

src/engine/scene.h

@@ -13,7 +13,7 @@ struct Scene {
 	const Solid* solid;
 };
 
-Scene* currentScene;
+extern Scene* currentScene;
 
 Scene* newScene();
 void insertChildScene(Scene* scene, Scene* newChild);

src/game/level.h

@@ -26,7 +26,7 @@ typedef struct {
 
 #define BLOCKGRID_CELL_SIZE 2.5f
 
-BlockGrid levelGrid;
+extern BlockGrid levelGrid;
 
 void initLevel();
 void startLevel();

src/game/player.h

@@ -5,7 +5,7 @@
 
 #include "engine/scene.h"
 
-Scene* playerCharacter;
+extern Scene* playerCharacter;
 
 void initPlayer();
 void spawnPlayer(Transform transform);