libclang: introduce cxstring::{createRef,createDup} for C strings

Also migrate all clients from the old API.

llvm-svn: 174238
diff --git a/clang/tools/libclang/CXCompilationDatabase.cpp b/clang/tools/libclang/CXCompilationDatabase.cpp
index 7fb5f24..0c63d17 100644
--- a/clang/tools/libclang/CXCompilationDatabase.cpp
+++ b/clang/tools/libclang/CXCompilationDatabase.cpp
@@ -110,7 +110,7 @@
     return cxstring::createNull();
 
   CompileCommand *cmd = static_cast<CompileCommand *>(CCmd);
-  return createCXString(cmd->Directory.c_str(), /*DupString=*/false);
+  return cxstring::createRef(cmd->Directory.c_str());
 }
 
 unsigned
@@ -133,7 +133,7 @@
   if (Arg >= Cmd->CommandLine.size())
     return cxstring::createNull();
 
-  return createCXString(Cmd->CommandLine[Arg].c_str(), /*DupString=*/false);
+  return cxstring::createRef(Cmd->CommandLine[Arg].c_str());
 }