[IRGen] Add convenience to define transient types.

Expose the createStructType helper to clients of IRGenModule which want
to define types which won't ever be used elsewhere.  This is just a
convenience--such clients could already have directly used the API on
llvm::Module directly.

Author: nate-chandler

lib/IRGen/IRGenModule.cpp

@@ -91,6 +91,11 @@ static llvm::StructType *createStructType(IRGenModule &IGM,
                                   name, packed);
 }
 
+llvm::StructType *IRGenModule::createTransientStructType(
+    StringRef name, std::initializer_list<llvm::Type *> types, bool packed) {
+  return createStructType(*this, name, types, packed);
+}
+
 static clang::CodeGenerator *createClangCodeGenerator(ASTContext &Context,
                                                       llvm::LLVMContext &LLVMContext,
                                                       const IRGenOptions &Opts,

lib/IRGen/IRGenModule.h

@@ -861,6 +861,11 @@ class IRGenModule {
   llvm::Constant *swiftImmortalRefCount = nullptr;
   llvm::Constant *swiftStaticArrayMetadata = nullptr;
 
+  llvm::StructType *
+  createTransientStructType(StringRef name,
+                            std::initializer_list<llvm::Type *> types,
+                            bool packed = false);
+
   /// Used to create unique names for class layout types with tail allocated
   /// elements.
   unsigned TailElemTypeID = 0;