[IRBuilder] Add additional overload with in-place Inserter construction (NFC)

Currently, for IRBuilders that require an explicitly constructed
Folder, we also force Inserter to be constructed and then copied.
Provide a variant where the Inserter uses in-place default
construction, to support cases where it is self-referential.

Author: nikic

llvm/include/llvm/IR/IRBuilder.h

@@ -2708,12 +2708,17 @@ class IRBuilder : public IRBuilderBase {
   InserterTy Inserter;
 
 public:
-  IRBuilder(LLVMContext &C, FolderTy Folder, InserterTy Inserter = InserterTy(),
+  IRBuilder(LLVMContext &C, FolderTy Folder, InserterTy Inserter,
             MDNode *FPMathTag = nullptr,
             ArrayRef<OperandBundleDef> OpBundles = {})
       : IRBuilderBase(C, this->Folder, this->Inserter, FPMathTag, OpBundles),
         Folder(Folder), Inserter(Inserter) {}
 
+  IRBuilder(LLVMContext &C, FolderTy Folder, MDNode *FPMathTag = nullptr,
+            ArrayRef<OperandBundleDef> OpBundles = {})
+      : IRBuilderBase(C, this->Folder, this->Inserter, FPMathTag, OpBundles),
+        Folder(Folder) {}
+
   explicit IRBuilder(LLVMContext &C, MDNode *FPMathTag = nullptr,
                      ArrayRef<OperandBundleDef> OpBundles = {})
       : IRBuilderBase(C, this->Folder, this->Inserter, FPMathTag, OpBundles) {}