build: opts-visitor is not really part of QAPI

It is only used by QEMU itself, do not build it into the tests.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

qapi/Makefile.objs

diff --git a/qapi/Makefile.objs b/qapi/Makefile.objs
index 5f5846e..f9bd3b9 100644
--- a/qapi/Makefile.objs
+++ b/qapi/Makefile.objs
@@ -1,3 +1,5 @@
 qapi-obj-y = qapi-visit-core.o qapi-dealloc-visitor.o qmp-input-visitor.o
 qapi-obj-y += qmp-output-visitor.o qmp-registry.o qmp-dispatch.o
-qapi-obj-y += string-input-visitor.o string-output-visitor.o opts-visitor.o
+qapi-obj-y += string-input-visitor.o string-output-visitor.o
+
+common-obj-y += opts-visitor.o