STYLE: report when skipping ThirdParty build

Allwmake

@@ -15,6 +15,8 @@ wmakeCheckPwd "$WM_PROJECT_DIR" || {
 if [ -d "$WM_THIRD_PARTY_DIR" ]
 then
     $WM_THIRD_PARTY_DIR/Allwmake
+else
+    echo "no ThirdParty sources found - skipping"
 fi
 
 # build OpenFOAM libraries and applications