build: add a "make modules" target

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/meson.build b/meson.build
index bc6234c..9b3fd4e 100644
--- a/meson.build
+++ b/meson.build
@@ -3285,6 +3285,9 @@
                 install: true,
                 install_dir: qemu_moddir)
 endforeach
+if emulator_modules.length() > 0
+  alias_target('modules', emulator_modules)
+endif
 
 softmmu_ss.add(authz, blockdev, chardev, crypto, io, qmp)
 common_ss.add(qom, qemuutil)