bugfix: reprEnum for enums with negative values

lib/system/repr.nim

@@ -59,7 +59,11 @@ proc reprChar(x: char): string {.compilerRtl.} =
 
 proc reprEnum(e: int, typ: PNimType): string {.compilerRtl.} =
   # we read an 'int' but this may have been too large, so mask the other bits:
-  let e = e and (1 shl (typ.size*8)-1)
+  let e = if typ.size == 1: e and 0xff
+          elif typ.size == 2: e and 0xffff
+          else: e
+  # XXX we need a proper narrowing based on signedness here
+  #e and ((1 shl (typ.size*8)) - 1)
   if ntfEnumHole notin typ.flags:
     if e <% typ.node.len:
       return $typ.node.sons[e].name