introduce --newruntime switch for the upcoming destructors and move semantics

compiler/options.nim

@@ -14,7 +14,6 @@ const
   hasTinyCBackend* = defined(tinyc)
   useEffectSystem* = true
   useWriteTracking* = false
-  newDestructors* = defined(nimV2)
   hasFFI* = defined(useFFI)
   newScopeForIf* = true
   useCaas* = not defined(noCaas)
@@ -145,6 +144,7 @@ var
   isServing*: bool = false
   gNoNimblePath* = false
   gExperimentalMode*: bool
+  newDestructors*: bool
 
 proc importantComments*(): bool {.inline.} = gCmd in {cmdDoc, cmdIdeTools}
 proc usesNativeGC*(): bool {.inline.} = gSelectedGC >= gcRefc