[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-nvptx64-nvidia-ubuntu` running on `as-builder-7` while building `llvm` at step 6 "test-build-unified-tree-check-llvm".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/160/builds/39262

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

```
Step 6 (test-build-unified-tree-check-llvm) failure: test (failure)
...
2.294 [3/9/791] Linking CXX executable unittests/Transforms/Vectorize/VectorizeTests
2.325 [3/8/792] Linking CXX executable unittests/Transforms/Vectorize/SandboxVectorizer/SandboxVectorizerTests
2.326 [3/7/793] Linking CXX executable unittests/IR/IRTests
2.342 [3/6/794] Linking CXX executable unittests/Transforms/Utils/UtilsTests
2.391 [3/5/795] Linking CXX executable unittests/tools/llvm-exegesis/LLVMExegesisTests
2.747 [3/4/796] Linking CXX executable unittests/ADT/ADTTests
2.796 [3/3/797] Linking CXX executable unittests/Support/SupportTests
9.789 [3/2/798] Building CXX object unittests/ObjectYAML/CMakeFiles/ObjectYAMLTests.dir/DXContainerYAMLTest.cpp.o
9.901 [2/2/799] Linking CXX executable unittests/ObjectYAML/ObjectYAMLTests
11.433 [2/1/800] Building CXX object unittests/CodeGen/CMakeFiles/CodeGenTests.dir/RematerializerTest.cpp.o
FAILED: unittests/CodeGen/CMakeFiles/CodeGenTests.dir/RematerializerTest.cpp.o 
CCACHE_CPP2=yes CCACHE_HASHDIR=yes CCACHE_SLOPPINESS=pch_defines,time_macros /usr/bin/ccache /usr/bin/c++ -DLLVM_BUILD_STATIC -D_DEBUG -D_GLIBCXX_ASSERTIONS -D_GLIBCXX_USE_CXX11_ABI=1 -D_GNU_SOURCE -D_LIBCPP_HARDENING_MODE=_LIBCPP_HARDENING_MODE_EXTENSIVE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -I/home/buildbot/worker/as-builder-7/llvm-nvptx64-nvidia-ubuntu/build/unittests/CodeGen -I/home/buildbot/worker/as-builder-7/llvm-nvptx64-nvidia-ubuntu/llvm-project/llvm/unittests/CodeGen -I/home/buildbot/worker/as-builder-7/llvm-nvptx64-nvidia-ubuntu/build/include -I/home/buildbot/worker/as-builder-7/llvm-nvptx64-nvidia-ubuntu/llvm-project/llvm/include -I/home/buildbot/worker/as-builder-7/llvm-nvptx64-nvidia-ubuntu/llvm-project/third-party/unittest/googletest/include -I/home/buildbot/worker/as-builder-7/llvm-nvptx64-nvidia-ubuntu/llvm-project/third-party/unittest/googlemock/include -fPIC -fno-semantic-interposition -fvisibility-inlines-hidden -Werror=date-time -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wno-missing-field-initializers -pedantic -Wno-long-long -Wimplicit-fallthrough -Wno-uninitialized -Wno-nonnull -Wno-class-memaccess -Wno-dangling-reference -Wno-redundant-move -Wno-pessimizing-move -Wno-array-bounds -Wno-stringop-overread -Wno-dangling-pointer -Wno-noexcept-type -Wdelete-non-virtual-dtor -Wsuggest-override -Wno-comment -Wno-misleading-indentation -Wctad-maybe-unsupported -fdiagnostics-color -ffunction-sections -fdata-sections -O3 -DNDEBUG -std=c++17 -UNDEBUG -Wno-dangling-else -Wno-variadic-macros -fno-exceptions -funwind-tables -fno-rtti -Wno-suggest-override -MD -MT unittests/CodeGen/CMakeFiles/CodeGenTests.dir/RematerializerTest.cpp.o -MF unittests/CodeGen/CMakeFiles/CodeGenTests.dir/RematerializerTest.cpp.o.d -o unittests/CodeGen/CMakeFiles/CodeGenTests.dir/RematerializerTest.cpp.o -c /home/buildbot/worker/as-builder-7/llvm-nvptx64-nvidia-ubuntu/llvm-project/llvm/unittests/CodeGen/RematerializerTest.cpp
/home/buildbot/worker/as-builder-7/llvm-nvptx64-nvidia-ubuntu/llvm-project/llvm/unittests/CodeGen/RematerializerTest.cpp: In static member function ‘static void {anonymous}::RematerializerTest::SetUpTestCase()’:
/home/buildbot/worker/as-builder-7/llvm-nvptx64-nvidia-ubuntu/llvm-project/llvm/unittests/CodeGen/RematerializerTest.cpp:96:5: error: ‘LLVMInitializeAMDGPUTargetInfo’ was not declared in this scope; did you mean ‘LLVMInitializeX86TargetInfo’?
   96 |     LLVMInitializeAMDGPUTargetInfo();
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      |     LLVMInitializeX86TargetInfo
/home/buildbot/worker/as-builder-7/llvm-nvptx64-nvidia-ubuntu/llvm-project/llvm/unittests/CodeGen/RematerializerTest.cpp:97:5: error: ‘LLVMInitializeAMDGPUTarget’ was not declared in this scope; did you mean ‘LLVMInitializeX86Target’?
   97 |     LLVMInitializeAMDGPUTarget();
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~
      |     LLVMInitializeX86Target
/home/buildbot/worker/as-builder-7/llvm-nvptx64-nvidia-ubuntu/llvm-project/llvm/unittests/CodeGen/RematerializerTest.cpp:98:5: error: ‘LLVMInitializeAMDGPUTargetMC’ was not declared in this scope; did you mean ‘LLVMInitializeX86TargetMC’?
   98 |     LLVMInitializeAMDGPUTargetMC();
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
      |     LLVMInitializeX86TargetMC
ninja: build stopped: subcommand failed.

```

</details>

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