TableGen: fix constness of new comparison function.

libc++ didn't seem to like a non-const call operator.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@190797 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/utils/TableGen/AsmMatcherEmitter.cpp b/utils/TableGen/AsmMatcherEmitter.cpp
index ff04d63..558090b 100644
--- a/utils/TableGen/AsmMatcherEmitter.cpp
+++ b/utils/TableGen/AsmMatcherEmitter.cpp
@@ -1065,7 +1065,7 @@
 }
 
 struct LessRegisterSet {
-  bool operator() (const RegisterSet &LHS, const RegisterSet & RHS) {
+  bool operator() (const RegisterSet &LHS, const RegisterSet & RHS) const {
     // std::set<T> defines its own compariso "operator<", but it
     // performs a lexicographical comparison by T's innate comparison
     // for some reason. We don't want non-deterministic pointer