xAODMuonCnv: cmake fixes

Declare an interface library for exported headers.

Event/xAOD/xAODMuonCnv/CMakeLists.txt

@@ -20,12 +20,16 @@ atlas_depends_on_subdirs( PUBLIC
                           Reconstruction/Particle
 			  Event/xAOD/xAODTruth )
 
+atlas_add_library( xAODMuonCnvLib
+                   xAODMuonCnv/*.h
+                   INTERFACE
+                   PUBLIC_HEADERS xAODMuonCnv
+                   LINK_LIBRARIES GaudiKernel xAODMuon MuonSegment TrkSegment AthLinks )
+
 # Component(s) in the package:
 atlas_add_component( xAODMuonCnv
                      src/*.cxx
                      src/components/*.cxx
-                     LINK_LIBRARIES AthLinks xAODMuon MuonSegment TrkSegment AthenaBaseComps AthenaKernel xAODPrimitives GaudiKernel muonEvent Particle xAODTruth)
+                     LINK_LIBRARIES xAODMuonCnvLib AthenaBaseComps AthenaKernel xAODPrimitives muonEvent Particle xAODTruth)
 
-# Install files from the package:
-atlas_install_headers( xAODMuonCnv )