balance Genode CPU pinning, deadlock at Genode exit (#6317)

* Genode: balance thread CPU affinities
Genode threads are pinned by defaut to the same CPU as the initial
component entrypoint thread. Thread affinities are also permanent. This
patch pins new threads to CPUs in a round-robin manner. Arbitrary CPU
pinning is not exposed and the 'nimPinToCpu' has no effect.

* Genode: guarantee that 'quit' will not return
On Genode exits are handled by whatever component is acting as parent.
The caller has no guarentee that the parent implementation will halt the
caller's threads, so explicitly deadlock the 'quit' procedure.

lib/system.nim

@@ -1435,7 +1435,8 @@ when defined(nimdoc):
 
 elif defined(genode):
   proc quit*(errorcode: int = QuitSuccess) {.magic: "Exit", noreturn,
-    importcpp: "genodeEnv->parent().exit(@)", header: "<base/env.h>".}
+    importcpp: "genodeEnv->parent().exit(@); Genode::sleep_forever()",
+    header: "<base/sleep.h>".}
 
 else:
   proc quit*(errorcode: int = QuitSuccess) {.