Based on result shown at:
<https://lab.llvm.org/buildbot/#/builders/216/builds/10120>
+# FIXME: The doubled backslashes occur under windows. That's almost surely a
+# lit issue beyond DEFINE/REDEFINE.
+
# Escape sequences that can appear in python re.sub replacement strings have no
# special meaning in the value.
# DEFINE: %{escape} = \g<0>\n
# RUN: echo '%{escape}'
-# CHECK: \g<0>\n
+# CHECK: {{\\?}}\g<0>{{\\?}}\n
# REDEFINE: %{escape} = \n \
# REDEFINE: \g<param>
# RUN: echo '%{escape}'
-# CHECK: \n \g<param>
+# CHECK: {{\\?}}\n {{\\?}}\g<param>
# CHECK: Passed: 1