utils: add a helper class to lit for captured substitutions

[compnerd]

Summary

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.

[rnk]

lgtm

utils/lit/lit/TestingConfig.py

157

Since there is no user of this in LLVM, can you put some example usage code in the docstring? In lit.cfg, use this code to create substitutions with regex backreferences:

config.substutions.append(('\b[^ ]*.cpp', SubstituteCaptures('\0.txt')))

[zturner]

utils/lit/lit/TestingConfig.py

157

Alternatively, add a lit lit test for it.

[compnerd]

SVN r327082

utils/lit/lit/TestingConfig.py

         else:
             return self.parent.root
 
+class SubstituteCaptures:
+    '''
+    Helper class to indicate that the substitutions contains backreferences.
+    '''
+    def __init__(self, substitution):
+        self.substitution = substitution
+
+    def replace(self, pattern, replacement):
+        return self.substitution
+
+    def __str__(self):
+        return self.substitution
+