[Orc] fixes "streams.readDataStr segafaults" when accepting a string literal (#20019) [backport]

fixes streams.readDataStr accept a string literal

(cherry picked from commit 286fcef68e)

lib/pure/streams.nim

@@ -1194,6 +1194,11 @@ else: # after 1.3 or JS not defined
 
   proc ssReadDataStr(s: Stream, buffer: var string, slice: Slice[int]): int =
     var s = StringStream(s)
+    when nimvm:
+      discard
+    else:
+      when declared(prepareMutation):
+        prepareMutation(buffer) # buffer might potentially be a CoW literal with ARC
     result = min(slice.b + 1 - slice.a, s.data.len - s.pos)
     if result > 0:
       jsOrVmBlock: