Update re2

third_party/re2/re2/unicode_casefold.h

Index: third_party/re2/re2/unicode_casefold.h
diff --git a/third_party/re2/re2/unicode_casefold.h b/third_party/re2/re2/unicode_casefold.h
index 160b07ea6ad07017dfd87a9fa2160330b0975c33..167114049ff0106ef0fa4a6038058a33fbd156ff 100644
--- a/third_party/re2/re2/unicode_casefold.h
+++ b/third_party/re2/re2/unicode_casefold.h
@@ -51,24 +51,24 @@ enum {
 };
 
 struct CaseFold {
-  uint32 lo;
-  uint32 hi;
+  Rune lo;
+  Rune hi;
   int32 delta;
 };
 
-extern CaseFold unicode_casefold[];
-extern int num_unicode_casefold;
+extern const CaseFold unicode_casefold[];
+extern const int num_unicode_casefold;
 
-extern CaseFold unicode_tolower[];
-extern int num_unicode_tolower;
+extern const CaseFold unicode_tolower[];
+extern const int num_unicode_tolower;
 
 // Returns the CaseFold* in the tables that contains rune.
 // If rune is not in the tables, returns the first CaseFold* after rune.
 // If rune is larger than any value in the tables, returns NULL.
-extern CaseFold* LookupCaseFold(CaseFold*, int, Rune rune);
+extern const CaseFold* LookupCaseFold(const CaseFold*, int, Rune rune);
 
 // Returns the result of applying the fold f to the rune r.
-extern Rune ApplyFold(CaseFold *f, Rune r);
+extern Rune ApplyFold(const CaseFold *f, Rune r);
 
 }  // namespace re2