utils: add a helper class to lit for captured substitutions

On Windows, if the substitution contains a back reference, it would
removed due to the replacement of the escape character in lit. Create a
helper class to avoid this which will simply ignore the replacement and
mark the substitution as having capture groups being referenced.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@327082 91177308-0d34-0410-b5e6-96231b3b80d8

Author: compnerd

utils/lit/lit/TestingConfig.py

@@ -152,3 +152,22 @@ def root(self):
         else:
             return self.parent.root
 
+class SubstituteCaptures:
+    """
+    Helper class to indicate that the substitutions contains backreferences.
+
+    This can be used as the following in lit.cfg to mark subsitutions as having
+    back-references::
+
+        config.substutions.append(('\b[^ ]*.cpp', SubstituteCaptures('\0.txt')))
+
+    """
+    def __init__(self, substitution):
+        self.substitution = substitution
+
+    def replace(self, pattern, replacement):
+        return self.substitution
+
+    def __str__(self):
+        return self.substitution
+