UniRec output: fix broken build on EL9 systems caused by changes to CMake defaults when building rpm

This has already been fixed in the main ipfixcol2 spec file earlier

See commit fcc1596 or https://www.spinics.net/lists/fedora-devel/msg272948.html for more info

Author: sedmicha

extra_plugins/output/unirec/ipfixcol2-unirec-output.spec.in

@@ -30,6 +30,7 @@ Plugin for converting IPFIX data to UniRec format.
 
 # Build source code
 %build
+%global _vpath_builddir .
 %cmake .
 make %{?_smp_mflags}