Add internal TLS support

Related to #970.

src/mir_init.c

@@ -190,9 +190,6 @@ int _glfwPlatformInit(void)
 
     createKeyTables();
 
-    if (!_glfwInitThreadLocalStoragePOSIX())
-        return GLFW_FALSE;
-
     if (!_glfwInitJoysticksLinux())
         return GLFW_FALSE;
 
@@ -222,7 +219,6 @@ void _glfwPlatformTerminate(void)
 {
     _glfwTerminateEGL();
     _glfwTerminateJoysticksLinux();
-    _glfwTerminateThreadLocalStoragePOSIX();
 
     _glfwDeleteEventQueueMir(_glfw.mir.eventQueue);