venus: allow to build vtest-only on non-DRM/KMS systems

The vtest backend doesn't require drm.

Backport-to: 25.1
Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/13420
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/36017>

src/virtio/vulkan/meson.build

@@ -74,12 +74,10 @@ libvn_files = files(
   'vn_ring.c',
   'vn_renderer_internal.c',
   'vn_renderer_util.c',
-  'vn_renderer_virtgpu.c',
   'vn_renderer_vtest.c',
 )
 
 vn_deps = [
-  dep_libdrm,
   dep_thread,
   idep_mesautil,
   idep_vulkan_util,
@@ -96,6 +94,11 @@ vn_flags = [
 
 vn_libs = []
 
+if system_has_kms_drm
+  libvn_files += files('vn_renderer_virtgpu.c')
+  vn_deps += dep_libdrm
+endif
+
 if with_platform_wayland or with_platform_x11 or \
    (system_has_kms_drm and not with_platform_android)
   libvn_files += files('vn_wsi.c')

src/virtio/vulkan/vn_renderer.h

@@ -218,10 +218,12 @@ struct vn_renderer {
    struct vn_renderer_sync_ops sync_ops;
 };
 
+#ifdef HAVE_LIBDRM
 VkResult
 vn_renderer_create_virtgpu(struct vn_instance *instance,
                            const VkAllocationCallbacks *alloc,
                            struct vn_renderer **renderer);
+#endif
 
 VkResult
 vn_renderer_create_vtest(struct vn_instance *instance,
@@ -233,6 +235,7 @@ vn_renderer_create(struct vn_instance *instance,
                    const VkAllocationCallbacks *alloc,
                    struct vn_renderer **renderer)
 {
+#ifdef HAVE_LIBDRM
    if (VN_DEBUG(VTEST)) {
       VkResult result = vn_renderer_create_vtest(instance, alloc, renderer);
       if (result == VK_SUCCESS)
@@ -240,6 +243,9 @@ vn_renderer_create(struct vn_instance *instance,
    }
 
    return vn_renderer_create_virtgpu(instance, alloc, renderer);
+#else
+   return vn_renderer_create_vtest(instance, alloc, renderer);
+#endif
 }
 
 static inline void