[libcxx] Have lexically_normal return the path with preferred separators

Differential Revision: https://reviews.llvm.org/D91179

GitOrigin-RevId: 513463fd266f059864ce3c0236494cced5de0f56
diff --git a/src/filesystem/operations.cpp b/src/filesystem/operations.cpp
index 458ba16..6f69ca9 100644
--- a/src/filesystem/operations.cpp
+++ b/src/filesystem/operations.cpp
@@ -1717,6 +1717,7 @@
   if (NeedTrailingSep)
     Result /= PS("");
 
+  Result.make_preferred();
   return Result;
 }