[clang] Replace SmallStr.str().str() with std::string conversion operator.
Use the std::string conversion operator introduced in
d7049213d0fcda691c9e79f9b41e357198d99738.
diff --git a/clang/lib/AST/Expr.cpp b/clang/lib/AST/Expr.cpp
index a0d11ee..51d29ae 100644
--- a/clang/lib/AST/Expr.cpp
+++ b/clang/lib/AST/Expr.cpp
@@ -856,7 +856,7 @@
 
     Out << Proto;
 
-    return Name.str().str();
+    return std::string(Name);
   }
   if (const CapturedDecl *CD = dyn_cast<CapturedDecl>(CurrentDecl)) {
     for (const DeclContext *DC = CD->getParent(); DC; DC = DC->getParent())
@@ -887,7 +887,7 @@
     MD->getSelector().print(Out);
     Out <<  ']';
 
-    return Name.str().str();
+    return std::string(Name);
   }
   if (isa<TranslationUnitDecl>(CurrentDecl) && IK == PrettyFunction) {
     // __PRETTY_FUNCTION__ -> "top level", the others produce an empty string.