demos: build both glfw and sdl

Apparently GLFW has a habit of not working on Wayland, because they
hard-code the platform at compile time. Might as well just provide all
four variants, who really cares about a few extra binaries?

The proper solution would be to make loading the windowing system
dynamic at runtime, but that probably requires handling command line
arguments and I can't really be bothered.

Also suppress a warning in the sdl code by rewriting it slightly.

demos/meson.build

@@ -24,44 +24,41 @@ nuklear = declare_dependency(
 
 apis = {}
 
-# Enable all supported combinations of API and windowing system, preferring
-# GLFW and falling back to SDL if the former is not supported
+# Enable all supported combinations of API and windowing system
 if glfw.found()
-
   if vulkan.found()
-    apis += {'vk': declare_dependency(
+    apis += {'glfw-vk': declare_dependency(
       sources: 'window_glfw.c',
       compile_args: '-DUSE_VK',
       dependencies: [libplacebo, vulkan, glfw],
     )}
   endif
 
   if opengl.found()
-    apis += {'gl': declare_dependency(
+    apis += {'glfw-gl': declare_dependency(
       sources: 'window_glfw.c',
       compile_args: '-DUSE_GL',
       dependencies: [libplacebo, glfw],
     )}
   endif
+endif
 
-elif sdl.found()
-
+if sdl.found()
   if vulkan.found()
-    apis += {'vk': declare_dependency(
+    apis += {'sdl-vk': declare_dependency(
       sources: 'window_sdl.c',
       compile_args: '-DUSE_VK',
       dependencies: [libplacebo, vulkan, sdl],
     )}
   endif
 
   if opengl.found()
-    apis += {'gl': declare_dependency(
+    apis += {'sdl-gl': declare_dependency(
       sources: 'window_sdl.c',
       compile_args: '-DUSE_GL',
       dependencies: [libplacebo, sdl],
     )}
   endif
-
 endif
 
 if apis.keys().length() == 0

demos/window_sdl.c

@@ -73,12 +73,9 @@ struct window *window_create(struct pl_context *ctx, const char *title,
     }
 
     const char **exts = malloc(num * sizeof(const char *));
+    SDL_Vulkan_GetInstanceExtensions(p->win, &num, exts);
     iparams.extensions = exts;
     iparams.num_extensions = num;
-    assert(exts);
-
-    bool ok = SDL_Vulkan_GetInstanceExtensions(p->win, &num, exts);
-    assert(ok);
 
     p->vk_inst = pl_vk_inst_create(ctx, &iparams);
     free(exts);