replace old problematic isNamedTuple implementation by TypeTrait isNamedTuple in dollars.nim (#13347)

* replace old problematic isNamedTuple implementation by TypeTrait isNamedTuple

* fix for bootstrap

compiler/condsyms.nim

@@ -103,6 +103,7 @@ proc initDefines*(symbols: StringTableRef) =
   defineSymbol("nimNewShiftOps")
   defineSymbol("nimHasCursor")
   defineSymbol("nimHasExceptionsQuery")
+  defineSymbol("nimHasIsNamedTuple")
 
   when defined(nimHasLibFFI):
     # Renaming as we can't conflate input vs output define flags; e.g. this

lib/system/dollars.nim

@@ -49,7 +49,10 @@ proc `$`*(t: typedesc): string {.magic: "TypeTrait".}
   ##   doAssert $(type("Foo")) == "string"
   ##   static: doAssert $(type(@['A', 'B'])) == "seq[char]"
 
-
+when defined(nimHasIsNamedTuple):
+  proc isNamedTuple(T: typedesc): bool {.magic: "TypeTrait".}
+else:
+  # for bootstrap; remove after release 1.2
   proc isNamedTuple(T: typedesc): bool =
     # Taken from typetraits.
     when T isnot tuple: result = false
@@ -62,6 +65,7 @@ proc isNamedTuple(T: typedesc): bool =
           return true
       return false
 
+
 proc `$`*[T: tuple|object](x: T): string =
   ## Generic ``$`` operator for tuples that is lifted from the components
   ## of `x`. Example: