Expect 4006 to fail on msys

In the 65001 codepage, we can't even cat the expected output on msys:
$ cat 4006.stdout
It works here
cat: write error: Permission denied

1 files changed, 12 insertions, 0 deletions

diff --git a/testsuite/driver/testlib.py b/testsuite/driver/testlib.py
index 0dce28c4aa..f48b86df81 100644
--- a/testsuite/driver/testlib.py
+++ b/testsuite/driver/testlib.py
@@ -278,6 +278,18 @@ def if_wordsize( ws, f ):
     else:
         return normal
 
+def if_msys( f ):
+    if config.msys:
+        return f
+    else:
+        return normal
+
+def if_cygwin( f ):
+    if config.cygwin:
+        return f
+    else:
+        return normal
+
 # ---
 
 def if_in_tree_compiler( f ):