docs: Serialize running apibuild.py

Use a witness file approach like we do for python/generator.py,
as suggested by Eric. Fixes the build issue reported here:

https://www.redhat.com/archives/libvir-list/2012-April/msg01435.htmlSigned-off-by: NCole Robinson <crobinso@redhat.com>

.gitignore

@@ -54,6 +54,7 @@
 /daemon/libvirtd.init
 /daemon/libvirtd.pod
 /daemon/libvirtd.service
+/docs/apibuild.py.stamp
 /docs/devhelp/libvirt.devhelp
 /docs/hvsupport.html.in
 /docs/libvirt-api.xml

docs/Makefile.am

@@ -200,12 +200,19 @@ python_generated_files = \
 		$(srcdir)/libvirt-qemu-api.xml \
 		$(srcdir)/libvirt-qemu-refs.xml
 
-$(python_generated_files): $(srcdir)/apibuild.py \
+APIBUILD="$(srcdir)/apibuild.py"
+APIBUILD_STAMP="$(APIBUILD).stamp"
+
+$(python_generated_files): $(APIBUILD_STAMP)
+
+$(APIBUILD_STAMP): $(srcdir)/apibuild.py \
 		$(srcdir)/../include/libvirt/*.h \
 		$(srcdir)/../src/libvirt.c \
 		$(srcdir)/../src/libvirt-qemu.c \
 		$(srcdir)/../src/util/virterror.c
-	$(AM_V_GEN)srcdir=$(srcdir) $(PYTHON) $(srcdir)/apibuild.py
+	$(AM_V_GEN)srcdir=$(srcdir) $(PYTHON) $(APIBUILD)
+	touch $@
+
 
 check-local: all
 
@@ -215,6 +222,7 @@ clean-local:
 maintainer-clean-local: clean-local
 	rm -rf $(srcdir)/libvirt-api.xml $(srcdir)/libvirt-refs.xml todo.html.in hvsupport.html.in
 	rm -rf $(srcdir)/libvirt-qemu-api.xml $(srcdir)/libvirt-qemu-refs.xml
+	rm -rf $(APIBUILD_STAMP)
 
 rebuild: api qemu_api all