If virgl and opengl are not available, the build process creates a useless
libvirtio-vga-gl module that does not have any device in it.  Follow the
example of virtio-vga-rutabaga and do not build the module at all in that
case.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 hw/display/meson.build | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/hw/display/meson.build b/hw/display/meson.build
index 7893b94c8ee..7db05eace97 100644
--- a/hw/display/meson.build
+++ b/hw/display/meson.build
@@ -125,12 +125,14 @@ if config_all_devices.has_key('CONFIG_VIRTIO_VGA')
                                          if_false: files('acpi-vga-stub.c'))
   hw_display_modules += {'virtio-vga': virtio_vga_ss}
 
-  virtio_vga_gl_ss = ss.source_set()
-  virtio_vga_gl_ss.add(when: ['CONFIG_VIRTIO_VGA', virgl, opengl],
-                       if_true: [files('virtio-vga-gl.c'), pixman])
-  virtio_vga_gl_ss.add(when: 'CONFIG_ACPI', if_true: files('acpi-vga.c'),
-                                            if_false: files('acpi-vga-stub.c'))
-  hw_display_modules += {'virtio-vga-gl': virtio_vga_gl_ss}
+  if virgl.found() and opengl.found()
+    virtio_vga_gl_ss = ss.source_set()
+    virtio_vga_gl_ss.add(when: ['CONFIG_VIRTIO_VGA', virgl, opengl],
+                         if_true: [files('virtio-vga-gl.c'), pixman])
+    virtio_vga_gl_ss.add(when: 'CONFIG_ACPI', if_true: files('acpi-vga.c'),
+                                              if_false: files('acpi-vga-stub.c'))
+    hw_display_modules += {'virtio-vga-gl': virtio_vga_gl_ss}
+  endif
 
   if rutabaga.found()
     virtio_vga_rutabaga_ss = ss.source_set()
-- 
2.44.0