[DWARF][dsymutil][llvm-dwarfutil] Create a placeholder library DWARFLinkerParallel.

[avl]

Summary

This patch is extracted from D96035. It creates an empty library DWARFLinkerParallel.

[avl]

rebased.

[JDevlieghere]

[begin bikeshedding]
I'm not sure how quickly dsymutil would be able to start using the "next" dwarf linker, so I think something like "DwarfLinkerParallel" or something like that might be more descriptive?
[end bikeshedding]

[avl]

addressed comments. renamed DWARFLinkerNext -> DWARFLinkerParallel

[JDevlieghere]

Thanks!

llvm/include/llvm/DWARFLinkerNext/DWARFLinker.h

+//===- DWARFLinker.h --------------------------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_DWARFLINKERNEXT_DWARFLINKER_H
+#define LLVM_DWARFLINKERNEXT_DWARFLINKER_H
+
+namespace llvm {
+namespace dwarflinker {} // end namespace dwarflinker
+} // end namespace llvm
+
+#endif // LLVM_DWARFLINKERNEXT_DWARFLINKER_H

llvm/lib/CMakeLists.txt

 include(LLVM-Build)
 
 # `Demangle', `Support' and `TableGen' libraries are added on the top-level
 # CMakeLists.txt
 
 add_subdirectory(IR)
 add_subdirectory(FuzzMutate)
 add_subdirectory(FileCheck)
 add_subdirectory(InterfaceStub)
 add_subdirectory(IRPrinter)
 add_subdirectory(IRReader)
 add_subdirectory(CodeGen)
 add_subdirectory(BinaryFormat)
 add_subdirectory(Bitcode)
 add_subdirectory(Bitstream)
 add_subdirectory(DWARFLinker)
+add_subdirectory(DWARFLinkerNext)
 add_subdirectory(Extensions)
 add_subdirectory(Frontend)
 add_subdirectory(Transforms)
 add_subdirectory(Linker)
 add_subdirectory(Analysis)
 add_subdirectory(LTO)
 add_subdirectory(MC)
 add_subdirectory(MCA)

llvm/lib/DWARFLinkerNext/CMakeLists.txt

+add_llvm_component_library(LLVMDWARFLinkerNext
+  DWARFLinker.cpp
+
+  ADDITIONAL_HEADER_DIRS
+  ${LLVM_MAIN_INCLUDE_DIR}/llvm/DWARFLinkerNext
+
+  DEPENDS
+  intrinsics_gen
+
+  LINK_COMPONENTS
+  BinaryFormat
+  DebugInfoDWARF
+  AsmPrinter
+  CodeGen
+  MC
+  Object
+  Support
+)

llvm/lib/DWARFLinkerNext/DWARFLinker.cpp

+//=== DWARFLinker.cpp -----------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/DWARFLinkerNext/DWARFLinker.h"
+
+namespace llvm {
+namespace dwarflinker {} // end of namespace dwarflinker
+} // namespace llvm

llvm/tools/dsymutil/CMakeLists.txt

 set(LLVM_TARGET_DEFINITIONS Options.td)
 tablegen(LLVM Options.inc -gen-opt-parser-defs)
 add_public_tablegen_target(DsymutilTableGen)
 
 set(LLVM_LINK_COMPONENTS
   AllTargetsCodeGens
   AllTargetsDescs
   AllTargetsInfos
   AsmPrinter
   DebugInfoDWARF
   DWARFLinker
+  DWARFLinkerNext
   MC
   Object
   CodeGen
   Option
   Remarks
   Support
   Target
   TargetParser

llvm/tools/llvm-dwarfutil/CMakeLists.txt

 set(LLVM_TARGET_DEFINITIONS Options.td)
 tablegen(LLVM Options.inc -gen-opt-parser-defs)
 add_public_tablegen_target(DwarfutilTableGen)
 
 set(LLVM_LINK_COMPONENTS
   DebugInfoDWARF
   DWARFLinker
+  DWARFLinkerNext
   MC
   ObjCopy
   Object
   Option
   Support
   Target
   TargetParser
   AllTargetsCodeGens