vici: Support ruby gem out-of-tree builds

Referencing $(srcdir) in the gemspec is not really an option, as "gem build"
includes the full path in the gem, so we need to build in $(srcdir). As there
does not seem to be a way to control the output of "gem build", we manually
move the gem to $(builddir) in OOT builds.

src/libcharon/plugins/vici/ruby/Makefile.am

@@ -6,7 +6,9 @@ vici.gemspec: $(srcdir)/vici.gemspec.in
 	$(srcdir)/vici.gemspec.in > $@
 
 vici-$(PACKAGE_VERSION).gem: vici.gemspec
-	$(GEM) build vici.gemspec
+	(cd $(srcdir); $(GEM) build $(abs_builddir)/vici.gemspec)
+	[ "$(srcdir)" = "$(builddir)" ] || \
+		mv $(srcdir)/vici-$(PACKAGE_VERSION).gem $(builddir)
 
 all-local: vici-$(PACKAGE_VERSION).gem