libclang: add new StringSet type

This allows the return of a set of CXStrings from libclang.  This is setup work
for an upcoming change to permit returning multiple mangled symbols.

llvm-svn: 252852
diff --git a/clang/tools/libclang/CXString.h b/clang/tools/libclang/CXString.h
index 72ac0cf..6473eb2 100644
--- a/clang/tools/libclang/CXString.h
+++ b/clang/tools/libclang/CXString.h
@@ -68,6 +68,8 @@
 /// \brief Create a CXString object that is backed by a string buffer.
 CXString createCXString(CXStringBuf *buf);
 
+CXStringSet *createSet(const std::vector<std::string> &Strings);
+
 /// \brief A string pool used for fast allocation/deallocation of strings.
 class CXStringPool {
 public: