[llvm] [CodeGen] Refactor rematerializer unit tests to reduce boilerplate (NFC) (PR #197575)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `llvm-clang-x86_64-sie-win` running on `sie-win-worker` while building `llvm` at step 7 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/46/builds/36411

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 7 (test-build-unified-tree-check-all) failure: test (failure)
...
[1234/1257] Linking CXX executable unittests\tools\llvm-profgen\LLVMProfgenTests.exe
[1235/1257] Linking CXX executable unittests\tools\llvm-profdata\LLVMProfdataTests.exe
[1236/1257] Linking CXX executable unittests\ExecutionEngine\MCJIT\MCJITTests.exe
[1237/1257] Linking CXX executable unittests\Transforms\Vectorize\VectorizeTests.exe
[1238/1257] Linking CXX executable unittests\Transforms\IPO\IPOTests.exe
[1239/1257] Linking CXX executable unittests\IR\IRTests.exe
[1240/1257] Linking CXX executable unittests\Passes\PassBuilderBindings\PassesBindingsTests.exe
[1241/1257] Linking CXX executable unittests\Transforms\Vectorize\SandboxVectorizer\SandboxVectorizerTests.exe
[1242/1257] Linking CXX executable unittests\tools\llvm-cfi-verify\CFIVerifyTests.exe
[1243/1257] Building CXX object unittests\CodeGen\CMakeFiles\CodeGenTests.dir\RematerializerTest.cpp.obj
FAILED: unittests/CodeGen/CMakeFiles/CodeGenTests.dir/RematerializerTest.cpp.obj 
C:\bin\ccache.exe C:\PROGRA~2\MICROS~1\2019\BUILDT~1\VC\Tools\MSVC\1429~1.301\bin\HostX64\x64\cl.exe  /nologo /TP -DLLVM_BUILD_STATIC -DUNICODE -D_CRT_NONSTDC_NO_DEPRECATE -D_CRT_NONSTDC_NO_WARNINGS -D_CRT_SECURE_NO_DEPRECATE -D_CRT_SECURE_NO_WARNINGS -D_GLIBCXX_ASSERTIONS -D_HAS_EXCEPTIONS=0 -D_LIBCPP_HARDENING_MODE=_LIBCPP_HARDENING_MODE_EXTENSIVE -D_SCL_SECURE_NO_DEPRECATE -D_SCL_SECURE_NO_WARNINGS -D_UNICODE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -Iunittests\CodeGen -IZ:\b\llvm-clang-x86_64-sie-win\llvm-project\llvm\unittests\CodeGen -Iinclude -IZ:\b\llvm-clang-x86_64-sie-win\llvm-project\llvm\include -IZ:\b\llvm-clang-x86_64-sie-win\llvm-project\third-party\unittest\googletest\include -IZ:\b\llvm-clang-x86_64-sie-win\llvm-project\third-party\unittest\googlemock\include /DWIN32 /D_WINDOWS   /Zc:inline /Zc:preprocessor /Zc:__cplusplus /Oi /bigobj /permissive- /W4 -wd4146 -wd4244 -wd4267 -wd4456 -wd4457 -wd4458 -wd4459 -wd4624 -wd4100 -wd4127 -wd4505 -wd4702 -wd4245 -wd4310 -wd4701 -wd4703 -wd4389 -wd4805 -wd4577 -wd4319 -wd4324 -wd4251 -wd4275 -w14062 -we4238 /Gw /O2 /Ob2  -MD -UNDEBUG /EHs-c- /GR- -std:c++17 /showIncludes /Founittests\CodeGen\CMakeFiles\CodeGenTests.dir\RematerializerTest.cpp.obj /Fdunittests\CodeGen\CMakeFiles\CodeGenTests.dir\ /FS -c Z:\b\llvm-clang-x86_64-sie-win\llvm-project\llvm\unittests\CodeGen\RematerializerTest.cpp
Z:\b\llvm-clang-x86_64-sie-win\llvm-project\llvm\unittests\CodeGen\RematerializerTest.cpp(96): error C3861: 'LLVMInitializeAMDGPUTargetInfo': identifier not found
Z:\b\llvm-clang-x86_64-sie-win\llvm-project\llvm\unittests\CodeGen\RematerializerTest.cpp(97): error C3861: 'LLVMInitializeAMDGPUTarget': identifier not found
Z:\b\llvm-clang-x86_64-sie-win\llvm-project\llvm\unittests\CodeGen\RematerializerTest.cpp(98): error C3861: 'LLVMInitializeAMDGPUTargetMC': identifier not found
[1244/1257] Linking CXX executable unittests\Target\TargetMachineCTests.exe
[1245/1257] Linking CXX executable unittests\Transforms\Coroutines\CoroTests.exe
[1246/1257] Linking CXX executable unittests\Transforms\Instrumentation\InstrumentationTests.exe
[1247/1257] Linking CXX executable unittests\Transforms\Utils\UtilsTests.exe
[1248/1257] Linking CXX executable unittests\tools\llvm-mca\LLVMMCATests.exe
[1249/1257] Linking CXX executable unittests\Target\X86\X86Tests.exe
[1250/1257] Linking CXX executable unittests\tools\llvm-exegesis\LLVMExegesisTests.exe
[1251/1257] Linking CXX executable unittests\Transforms\Scalar\ScalarTests.exe
[1252/1257] Building CXX object unittests\ObjectYAML\CMakeFiles\ObjectYAMLTests.dir\DXContainerYAMLTest.cpp.obj
[1253/1257] Linking CXX executable tools\clang\unittests\AllClangUnitTests.exe
[1254/1257] Linking CXX executable tools\clang\unittests\Interpreter\ClangReplInterpreterTests.exe
ninja: build stopped: subcommand failed.

```

</details>

https://github.com/llvm/llvm-project/pull/197575