Check only for relevant Vulkan extensions

Related to #858.

src/internal.h

@@ -455,11 +455,16 @@ struct _GLFWlibrary
         PFN_vkGetInstanceProcAddr GetInstanceProcAddr;
 #endif
         GLFWbool        KHR_surface;
+#if defined(_GLFW_WIN32)
         GLFWbool        KHR_win32_surface;
+#elif defined(_GLFW_X11)
         GLFWbool        KHR_xlib_surface;
         GLFWbool        KHR_xcb_surface;
+#elif defined(_GLFW_WAYLAND)
         GLFWbool        KHR_wayland_surface;
+#elif defined(_GLFW_MIR)
         GLFWbool        KHR_mir_surface;
+#endif
     } vk;
 
     struct {

src/vulkan.c

@@ -108,16 +108,21 @@ GLFWbool _glfwInitVulkan(void)
     {
         if (strcmp(ep[i].extensionName, "VK_KHR_surface") == 0)
             _glfw.vk.KHR_surface = GLFW_TRUE;
+#if defined(_GLFW_WIN32)
         else if (strcmp(ep[i].extensionName, "VK_KHR_win32_surface") == 0)
             _glfw.vk.KHR_win32_surface = GLFW_TRUE;
+#elif defined(_GLFW_X11)
         else if (strcmp(ep[i].extensionName, "VK_KHR_xlib_surface") == 0)
             _glfw.vk.KHR_xlib_surface = GLFW_TRUE;
         else if (strcmp(ep[i].extensionName, "VK_KHR_xcb_surface") == 0)
             _glfw.vk.KHR_xcb_surface = GLFW_TRUE;
+#elif defined(_GLFW_WAYLAND)
         else if (strcmp(ep[i].extensionName, "VK_KHR_wayland_surface") == 0)
             _glfw.vk.KHR_wayland_surface = GLFW_TRUE;
+#elif defined(_GLFW_MIR)
         else if (strcmp(ep[i].extensionName, "VK_KHR_mir_surface") == 0)
             _glfw.vk.KHR_mir_surface = GLFW_TRUE;
+#endif
     }
 
     free(ep);