restore the compilation for Slovak, Croatian and Czech

src/croatian/ExtendHrv.gf

@@ -26,6 +26,8 @@ concrete ExtendHrv of Extend = CatHrv **
     ,ComplBareVS
     ,CompIQuant
     ,CompBareCN
+    ,PiedPipingQuestSlash
+    ,PiedPipingRelSlash
     ]
   with (Grammar = GrammarHrv)
     **

src/czech/ExtendCze.gf

@@ -25,6 +25,8 @@ concrete ExtendCze of Extend = CatCze **
     ,ComplBareVS
     ,CompIQuant
     ,CompBareCN
+    ,PiedPipingQuestSlash
+    ,PiedPipingRelSlash
     ]
   with (Grammar = GrammarCze)
     **

src/slovak/ExtendSlo.gf

@@ -25,6 +25,8 @@ concrete ExtendSlo of Extend = CatSlo **
     ,ComplBareVS
     ,CompIQuant
     ,CompBareCN
+    ,PiedPipingQuestSlash
+    ,PiedPipingRelSlash
     ]
   with (Grammar = GrammarSlo)
     **