[llvm-diff] Create libLLVMDiff library

[void]

Summary

Some tools may want to use the LLVM "diff" code. Move the code into a
library for easy use.

No functionality change intende.

[JonChesterfield]

CI is failing on:

Cannot find source file:
   llvm-livepatch.cpp

New file missing from this commit?

edit: precommit testing also failed on that, e.g. https://buildkite.com/llvm-project/premerge-checks/builds/50915#a9e6c562-ce15-448d-935f-b63a5d50555b

[dyung]

Was the llvm-livepatch changes intended to be part of this change?

[MaskRay]

A new tool llvm-livepatch probably needs a discussion on llvm-dev...

llvm/tools/llvm-diff/CMakeLists.txt

 set(LLVM_LINK_COMPONENTS
   Core
   IRReader
   Support
   )
 
 add_llvm_tool(llvm-diff
   llvm-diff.cpp
-  DiffConsumer.cpp
-  DiffLog.cpp
-  DifferenceEngine.cpp
 
   DEPENDS
   intrinsics_gen
   )
+
+add_subdirectory(lib)
+target_link_libraries(llvm-diff PRIVATE LLVMDiff)

llvm/tools/llvm-diff/lib/CMakeLists.txt

+set(LLVM_LINK_COMPONENTS
+    Core
+    Support
+    )
+
+add_llvm_library(LLVMDiff
+  STATIC
+  DiffConsumer.cpp
+  DiffConsumer.h
+  DifferenceEngine.cpp
+  DifferenceEngine.h
+  DiffLog.cpp
+  DiffLog.h
+  )

llvm/tools/llvm-diff/llvm-diff.cpp

 //===-- llvm-diff.cpp - Module comparator command-line driver ---*- 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
 //
 //===----------------------------------------------------------------------===//
 //
 // This file defines the command-line driver for the difference engine.
 //
 //===----------------------------------------------------------------------===//
 
-#include "DiffLog.h"
-#include "DifferenceEngine.h"
+#include "lib/DiffLog.h"
+#include "lib/DifferenceEngine.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/IR/LLVMContext.h"
 #include "llvm/IR/Module.h"
 #include "llvm/IR/Type.h"
 #include "llvm/IRReader/IRReader.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/SourceMgr.h"

llvm/tools/llvm-livepatch/CMakeLists.txt

+set(LLVM_LINK_COMPONENTS
+  Core
+  IRReader
+  Support
+  )
+
+add_llvm_tool(llvm-livepatch
+  llvm-livepatch.cpp
+
+  DEPENDS
+  intrinsics_gen
+  )