[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-win-fast` running on `as-builder-3` while building `llvm` at step 7 "test-build-unified-tree-check-llvm-unit".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/2/builds/53406

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

```
Step 7 (test-build-unified-tree-check-llvm-unit) failure: test (failure)
...
[805/821] Linking CXX executable unittests\Passes\PassBuilderBindings\PassesBindingsTests.exe
[806/821] Linking CXX executable unittests\IR\IRTests.exe
[807/821] Linking CXX executable unittests\Transforms\Vectorize\SandboxVectorizer\SandboxVectorizerTests.exe
[808/821] Linking CXX executable unittests\Transforms\Vectorize\VectorizeTests.exe
[809/821] Linking CXX executable unittests\Transforms\IPO\IPOTests.exe
[810/821] Linking CXX executable unittests\Target\TargetMachineCTests.exe
[811/821] Linking CXX executable unittests\Target\ARM\ARMTests.exe
[812/821] Linking CXX executable unittests\tools\llvm-exegesis\LLVMExegesisTests.exe
[813/821] Linking CXX executable unittests\Transforms\Coroutines\CoroTests.exe
[814/821] Building CXX object unittests\CodeGen\CMakeFiles\CodeGenTests.dir\RematerializerTest.cpp.obj
FAILED: unittests/CodeGen/CMakeFiles/CodeGenTests.dir/RematerializerTest.cpp.obj 
C:\ninja\ccache.exe C:\PROGRA~1\MICROS~2\2022\COMMUN~1\VC\Tools\MSVC\1444~1.352\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_HAS_EXCEPTIONS=0 -D_SCL_SECURE_NO_DEPRECATE -D_SCL_SECURE_NO_WARNINGS -D_UNICODE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -IC:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\build\unittests\CodeGen -IC:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\llvm-project\llvm\unittests\CodeGen -IC:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\build\include -IC:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\llvm-project\llvm\include -IC:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\llvm-project\third-party\unittest\googletest\include -IC:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\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 /DNDEBUG -MD /EHs-c- /GR- -std:c++17 /showIncludes /Founittests\CodeGen\CMakeFiles\CodeGenTests.dir\RematerializerTest.cpp.obj /Fdunittests\CodeGen\CMakeFiles\CodeGenTests.dir\ /FS -c C:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\llvm-project\llvm\unittests\CodeGen\RematerializerTest.cpp
C:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\llvm-project\llvm\unittests\CodeGen\RematerializerTest.cpp(96): error C3861: 'LLVMInitializeAMDGPUTargetInfo': identifier not found
C:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\llvm-project\llvm\unittests\CodeGen\RematerializerTest.cpp(97): error C3861: 'LLVMInitializeAMDGPUTarget': identifier not found
C:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\llvm-project\llvm\unittests\CodeGen\RematerializerTest.cpp(98): error C3861: 'LLVMInitializeAMDGPUTargetMC': identifier not found
[815/821] Linking CXX executable unittests\Transforms\Instrumentation\InstrumentationTests.exe
[816/821] Linking CXX executable unittests\Transforms\Utils\UtilsTests.exe
[817/821] Linking CXX executable unittests\Transforms\Scalar\ScalarTests.exe
[818/821] Building CXX object unittests\ObjectYAML\CMakeFiles\ObjectYAMLTests.dir\DXContainerYAMLTest.cpp.obj
ninja: build stopped: subcommand failed.

```

</details>

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