Fix documentations for declared (instead of defined)

compiler/semgnrc.nim

@@ -243,7 +243,7 @@ proc semGenericStmt(c: PContext, n: PNode,
     elif fn.kind == nkDotExpr:
       result.sons[0] = fuzzyLookup(c, fn, flags, ctx, mixinContext)
       first = 1
-    # Consider 'when defined(globalsSlot): ThreadVarSetValue(globalsSlot, ...)'
+    # Consider 'when declared(globalsSlot): ThreadVarSetValue(globalsSlot, ...)'
     # in threads.nim: the subtle preprocessing here binds 'globalsSlot' which 
     # is not exported and yet the generic 'threadProcWrapper' works correctly.
     let flags = if mixinContext: flags+{withinMixin} else: flags

lib/system.nim

@@ -124,7 +124,7 @@ proc declared*(x: expr): bool {.magic: "Defined", noSideEffect.}
   ## feature or not:
   ##
   ## .. code-block:: Nim
-  ##   when not defined(strutils.toUpper):
+  ##   when not declared(strutils.toUpper):
   ##     # provide our own toUpper proc here, because strutils is
   ##     # missing it.