[llvm] [MergeFunctions] Add support to run the pass over a set of function pointers (PR #111045)

[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/9215

<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)
...
0.983 [2/9/680] Linking CXX executable unittests/Transforms/Vectorize/SandboxVectorizer/SandboxVectorizerTests
1.017 [2/8/681] Linking CXX executable unittests/tools/llvm-exegesis/LLVMExegesisTests
1.026 [2/7/682] Linking CXX executable unittests/CodeGen/CodeGenTests
1.042 [2/6/683] Linking CXX executable unittests/Frontend/LLVMFrontendTests
1.099 [2/5/684] Linking CXX executable unittests/Analysis/AnalysisTests
1.205 [2/4/685] Linking CXX executable unittests/IR/IRTests
1.298 [2/3/686] Linking CXX executable unittests/Support/SupportTests
1.367 [2/2/687] Linking CXX executable unittests/ADT/ADTTests
4.496 [2/1/688] Building CXX object unittests/Transforms/Utils/CMakeFiles/UtilsTests.dir/MergeFunctionsTest.cpp.o
4.662 [1/1/689] Linking CXX executable unittests/Transforms/Utils/UtilsTests
FAILED: unittests/Transforms/Utils/UtilsTests 
: && /usr/bin/c++ -fPIC -fno-semantic-interposition -fvisibility-inlines-hidden -Werror=date-time -fno-lifetime-dse -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-redundant-move -Wno-pessimizing-move -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 -fuse-ld=gold     -Wl,--gc-sections unittests/Transforms/Utils/CMakeFiles/UtilsTests.dir/ASanStackFrameLayoutTest.cpp.o unittests/Transforms/Utils/CMakeFiles/UtilsTests.dir/BasicBlockUtilsTest.cpp.o unittests/Transforms/Utils/CMakeFiles/UtilsTests.dir/CallPromotionUtilsTest.cpp.o unittests/Transforms/Utils/CMakeFiles/UtilsTests.dir/CloningTest.cpp.o unittests/Transforms/Utils/CMakeFiles/UtilsTests.dir/CodeExtractorTest.cpp.o unittests/Transforms/Utils/CMakeFiles/UtilsTests.dir/CodeLayoutTest.cpp.o unittests/Transforms/Utils/CMakeFiles/UtilsTests.dir/CodeMoverUtilsTest.cpp.o unittests/Transforms/Utils/CMakeFiles/UtilsTests.dir/DebugifyTest.cpp.o unittests/Transforms/Utils/CMakeFiles/UtilsTests.dir/FunctionComparatorTest.cpp.o unittests/Transforms/Utils/CMakeFiles/UtilsTests.dir/IntegerDivisionTest.cpp.o unittests/Transforms/Utils/CMakeFiles/UtilsTests.dir/LocalTest.cpp.o unittests/Transforms/Utils/CMakeFiles/UtilsTests.dir/LoopRotationUtilsTest.cpp.o unittests/Transforms/Utils/CMakeFiles/UtilsTests.dir/LoopUtilsTest.cpp.o unittests/Transforms/Utils/CMakeFiles/UtilsTests.dir/MemTransferLowering.cpp.o unittests/Transforms/Utils/CMakeFiles/UtilsTests.dir/ModuleUtilsTest.cpp.o unittests/Transforms/Utils/CMakeFiles/UtilsTests.dir/MergeFunctionsTest.cpp.o unittests/Transforms/Utils/CMakeFiles/UtilsTests.dir/ScalarEvolutionExpanderTest.cpp.o unittests/Transforms/Utils/CMakeFiles/UtilsTests.dir/SizeOptsTest.cpp.o unittests/Transforms/Utils/CMakeFiles/UtilsTests.dir/SSAUpdaterBulkTest.cpp.o unittests/Transforms/Utils/CMakeFiles/UtilsTests.dir/UnrollLoopTest.cpp.o unittests/Transforms/Utils/CMakeFiles/UtilsTests.dir/ValueMapperTest.cpp.o unittests/Transforms/Utils/CMakeFiles/UtilsTests.dir/ProfDataUtilTest.cpp.o -o unittests/Transforms/Utils/UtilsTests  -Wl,-rpath,/home/buildbot/worker/as-builder-7/ramdisk/llvm-nvptx64-nvidia-ubuntu/build/lib  lib/libLLVMPasses.so.20.0git  lib/libllvm_gtest_main.so.20.0git  lib/libllvm_gtest.so.20.0git  lib/libLLVMBitWriter.so.20.0git  lib/libLLVMVectorize.so.20.0git  lib/libLLVMTransformUtils.so.20.0git  lib/libLLVMAnalysis.so.20.0git  lib/libLLVMProfileData.so.20.0git  lib/libLLVMAsmParser.so.20.0git  lib/libLLVMCore.so.20.0git  lib/libLLVMSupport.so.20.0git  -Wl,-rpath-link,/home/buildbot/worker/as-builder-7/ramdisk/llvm-nvptx64-nvidia-ubuntu/build/lib && :
unittests/Transforms/Utils/CMakeFiles/UtilsTests.dir/MergeFunctionsTest.cpp.o:MergeFunctionsTest.cpp:function (anonymous namespace)::MergeFunctions_TrueOutputModuleTest_Test::TestBody(): error: undefined reference to 'llvm::MergeFunctionsPass::runOnModule(llvm::Module&)'
unittests/Transforms/Utils/CMakeFiles/UtilsTests.dir/MergeFunctionsTest.cpp.o:MergeFunctionsTest.cpp:function (anonymous namespace)::MergeFunctions_FalseOutputModuleTest_Test::TestBody(): error: undefined reference to 'llvm::MergeFunctionsPass::runOnModule(llvm::Module&)'
unittests/Transforms/Utils/CMakeFiles/UtilsTests.dir/MergeFunctionsTest.cpp.o:MergeFunctionsTest.cpp:function (anonymous namespace)::MergeFunctions_TrueOutputFunctionsTest_Test::TestBody(): error: undefined reference to 'llvm::MergeFunctionsPass::runOnFunctions(llvm::ArrayRef<llvm::Function*>)'
unittests/Transforms/Utils/CMakeFiles/UtilsTests.dir/MergeFunctionsTest.cpp.o:MergeFunctionsTest.cpp:function (anonymous namespace)::MergeFunctions_FalseOutputFunctionsTest_Test::TestBody(): error: undefined reference to 'llvm::MergeFunctionsPass::runOnFunctions(llvm::ArrayRef<llvm::Function*>)'
collect2: error: ld returned 1 exit status
ninja: build stopped: subcommand failed.

```

</details>

https://github.com/llvm/llvm-project/pull/111045