[K/N] LLVM: Add missing opaque pointer API

LLVMConstGEP2 and LLVMConstInBoundsGEP2 were forward declared in
LLVM-11, but not implemented until LLVM-14. This patch adds these along
with the missing LLVMAddAlias2. All three implementations are copied
from llvm branch release/14.x

kotlin-native/libllvmext/src/main/cpp/OpaquePointerAPI.cpp

@@ -0,0 +1,37 @@
+#include "OpaquePointerAPI.h"
+
+#include <llvm/IR/IntrinsicInst.h>
+#include <llvm/IR/Module.h>
+
+using namespace llvm;
+
+/* These are the opaque pointer functions that are missing in llvm-11, which
+must be removed upon upgrading LLVM version.
+
+Copied from llvm release/14.x.
+*/
+
+LLVMValueRef LLVMAddAlias2(LLVMModuleRef M, LLVMTypeRef ValueTy,
+                           unsigned AddrSpace, LLVMValueRef Aliasee,
+                           const char *Name) {
+  return wrap(GlobalAlias::create(unwrap(ValueTy), AddrSpace,
+                                  GlobalValue::ExternalLinkage, Name,
+                                  unwrap<Constant>(Aliasee), unwrap(M)));
+}
+
+LLVMValueRef LLVMConstGEP2(LLVMTypeRef Ty, LLVMValueRef ConstantVal,
+                           LLVMValueRef *ConstantIndices, unsigned NumIndices) {
+  ArrayRef<Constant *> IdxList(unwrap<Constant>(ConstantIndices, NumIndices),
+                               NumIndices);
+  Constant *Val = unwrap<Constant>(ConstantVal);
+  return wrap(ConstantExpr::getGetElementPtr(unwrap(Ty), Val, IdxList));
+}
+
+LLVMValueRef LLVMConstInBoundsGEP2(LLVMTypeRef Ty, LLVMValueRef ConstantVal,
+                                   LLVMValueRef *ConstantIndices,
+                                   unsigned NumIndices) {
+  ArrayRef<Constant *> IdxList(unwrap<Constant>(ConstantIndices, NumIndices),
+                               NumIndices);
+  Constant *Val = unwrap<Constant>(ConstantVal);
+  return wrap(ConstantExpr::getInBoundsGetElementPtr(unwrap(Ty), Val, IdxList));
+}

kotlin-native/libllvmext/src/main/include/OpaquePointerAPI.h

@@ -0,0 +1,35 @@
+
+#ifndef LIBLLVMEXT_OPAQUE_POINTER_API_H
+#define LIBLLVMEXT_OPAQUE_POINTER_API_H
+
+#include <llvm-c/Core.h>
+#include <llvm-c/Target.h>
+
+# ifdef __cplusplus
+extern "C" {
+# endif
+
+/* These are the opaque pointer functions that are missing in llvm-11, which
+must be removed upon upgrading LLVM version.
+
+Copied from llvm release/14.x.
+*/
+
+// LLVMConstGEP2 and LLVMConstInBoundsGEP2 are already forward declared in Core.h
+LLVMValueRef LLVMConstGEP2(LLVMTypeRef Ty, LLVMValueRef ConstantVal,
+                           LLVMValueRef *ConstantIndices, unsigned NumIndices);
+
+LLVMValueRef LLVMConstInBoundsGEP2(LLVMTypeRef Ty, LLVMValueRef ConstantVal,
+                                   LLVMValueRef *ConstantIndices,
+                                   unsigned NumIndices);
+
+LLVMValueRef LLVMAddAlias2(LLVMModuleRef M, LLVMTypeRef ValueTy,
+                           unsigned AddrSpace, LLVMValueRef Aliasee,
+                           const char *Name);
+
+# ifdef __cplusplus
+}
+# endif
+
+#endif // LIBLLVMEXT_OPAQUE_POINTER_API_H
+