meson: convert wixl detection to Meson

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/meson_options.txt b/meson_options.txt
index 7dcd81c..95f1079 100644
--- a/meson_options.txt
+++ b/meson_options.txt
@@ -17,6 +17,8 @@
        description: 'install provided firmware blobs')
 option('sparse', type : 'feature', value : 'auto',
        description: 'sparse checker')
+option('guest_agent_msi', type : 'feature', value : 'auto',
+       description: 'Build MSI package for the QEMU Guest Agent')
 
 option('malloc_trim', type : 'feature', value : 'auto',
        description: 'enable libc malloc_trim() for memory optimization')