fixes #5143

lib/system/threads.nim

@@ -398,7 +398,7 @@ template afterThreadRuns() =
     threadDestructionHandlers[i]()
 
 when not defined(boehmgc) and not hasSharedHeap and not defined(gogc) and not defined(gcRegions):
-  proc deallocOsPages()
+  proc deallocOsPages() {.rtl.}
 
 when defined(boehmgc):
   type GCStackBaseProc = proc(sb: pointer, t: pointer) {.noconv.}