[ClangImporter] Use new CXXThisExpr::Create function

The constructor takes a new arg which `Create` now handles. Use it
instead.

Author: bnbarham

lib/ClangImporter/ClangDerivedConformances.cpp

@@ -264,8 +264,8 @@ instantiateTemplatedOperator(ClangImporter::Implementation &impl,
 
   clang::UnresolvedSet<1> ops;
   auto qualType = clang::QualType(classDecl->getTypeForDecl(), 0);
-  auto arg = new (clangCtx)
-      clang::CXXThisExpr(clang::SourceLocation(), qualType, false);
+  auto arg = clang::CXXThisExpr::Create(clangCtx, clang::SourceLocation(),
+                                        qualType, false);
   arg->setType(clang::QualType(classDecl->getTypeForDecl(), 0));
 
   clang::OverloadedOperatorKind opKind =

lib/ClangImporter/ClangImporter.cpp

@@ -5211,9 +5211,9 @@ static clang::CXXMethodDecl *synthesizeCxxBaseGetterAccessorMethod(
 
   // Returns the expression that accesses the base field from derived type.
   auto createFieldAccess = [&]() -> clang::Expr * {
-    auto *thisExpr = new (clangCtx)
-        clang::CXXThisExpr(clang::SourceLocation(), newMethod->getThisType(),
-                           /*IsImplicit=*/false);
+    auto *thisExpr = clang::CXXThisExpr::Create(
+        clangCtx, clang::SourceLocation(), newMethod->getThisType(),
+        /*IsImplicit=*/false);
     clang::QualType baseClassPtr = clangCtx.getRecordType(baseClass);
     baseClassPtr.addConst();
     baseClassPtr = clangCtx.getPointerType(baseClassPtr);

lib/ClangImporter/SwiftDeclSynthesizer.cpp

@@ -2114,8 +2114,9 @@ clang::CXXMethodDecl *SwiftDeclSynthesizer::synthesizeCXXForwardingMethod(
   auto diagState = clangSema.DelayedDiagnostics.push(diagPool);
 
   // Construct the method's body.
-  clang::Expr *thisExpr = new (clangCtx) clang::CXXThisExpr(
-      clang::SourceLocation(), newMethod->getThisType(), /*IsImplicit=*/false);
+  clang::Expr *thisExpr = clang::CXXThisExpr::Create(
+      clangCtx, clang::SourceLocation(), newMethod->getThisType(),
+      /*IsImplicit=*/false);
   if (castThisToNonConstThis) {
     auto baseClassPtr =
         clangCtx.getPointerType(clangCtx.getRecordType(derivedClass));