cleanup Ordinal (#13501)

lib/system.nim

@@ -87,6 +87,18 @@ proc defined*(x: untyped): bool {.magic: "Defined", noSideEffect, compileTime.}
   ##     # Do here programmer friendly expensive sanity checks.
   ##   # Put here the normal code
 
+when defined(nimHashOrdinalFixed):
+  type
+    Ordinal*[T] {.magic: Ordinal.} ## Generic ordinal type. Includes integer,
+                                   ## bool, character, and enumeration types
+                                   ## as well as their subtypes. See also
+                                   ## `SomeOrdinal`.
+else:
+  # bootstrap <= 0.20.0
+  type
+    OrdinalImpl[T] {.magic: Ordinal.}
+    Ordinal* = OrdinalImpl | uint | uint64
+
 when defined(nimHasRunnableExamples):
   proc runnableExamples*(body: untyped) {.magic: "RunnableExamples".}
     ## A section you should use to mark `runnable example`:idx: code with.