[llvm] [CodeGen] Expose the extensibility of PassConfig to plugins (PR #139059)

[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/20849

<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)
...
2.125 [2/9/703] Linking CXX executable unittests/Transforms/Scalar/ScalarTests
2.153 [2/8/704] Linking CXX executable unittests/Transforms/Vectorize/SandboxVectorizer/SandboxVectorizerTests
2.169 [2/7/705] Linking CXX executable unittests/IR/IRTests
2.175 [2/6/706] Linking CXX executable unittests/Transforms/Utils/UtilsTests
2.191 [2/5/707] Linking CXX executable unittests/ADT/ADTTests
2.220 [2/4/708] Linking CXX executable unittests/tools/llvm-exegesis/LLVMExegesisTests
2.599 [2/3/709] Linking CXX executable unittests/Support/SupportTests
5.002 [2/2/710] Building CXX object unittests/CodeGen/CGPluginTest/CMakeFiles/CGPluginTest.dir/Plugin/CodeGenTestPass.cpp.o
8.425 [2/1/711] Building CXX object unittests/CodeGen/CGPluginTest/CMakeFiles/CGPluginTest.dir/PluginTest.cpp.o
8.531 [1/1/712] Linking CXX executable unittests/CodeGen/CGPluginTest/CGPluginTest
FAILED: unittests/CodeGen/CGPluginTest/CGPluginTest 
: && /usr/bin/c++ -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-maybe-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,--export-dynamic   -Wl,--gc-sections unittests/CodeGen/CGPluginTest/CMakeFiles/CGPluginTest.dir/PluginTest.cpp.o unittests/CodeGen/CGPluginTest/CMakeFiles/CGPluginTest.dir/Plugin/CodeGenTestPass.cpp.o -o unittests/CodeGen/CGPluginTest/CGPluginTest  -Wl,-rpath,/home/buildbot/worker/as-builder-7/llvm-nvptx64-nvidia-ubuntu/build/lib  lib/libLLVMX86CodeGen.so.21.0git  lib/libLLVMX86AsmParser.so.21.0git  lib/libLLVMX86Desc.so.21.0git  lib/libLLVMX86Disassembler.so.21.0git  lib/libLLVMX86Info.so.21.0git  lib/libLLVMNVPTXCodeGen.so.21.0git  lib/libLLVMNVPTXDesc.so.21.0git  lib/libLLVMNVPTXInfo.so.21.0git  lib/libllvm_gtest_main.so.21.0git  lib/libLLVMTestingSupport.so.21.0git  lib/libLLVMCodeGen.so.21.0git  lib/libLLVMTarget.so.21.0git  lib/libLLVMCore.so.21.0git  lib/libllvm_gtest.so.21.0git  lib/libLLVMSupport.so.21.0git  -Wl,-rpath-link,/home/buildbot/worker/as-builder-7/llvm-nvptx64-nvidia-ubuntu/build/lib && :
unittests/CodeGen/CGPluginTest/CMakeFiles/CGPluginTest.dir/PluginTest.cpp.o:PluginTest.cpp:function CGPluginTests_ExecuteCallback_Test::TestBody() [clone .localalias]:(.text._ZN34CGPluginTests_ExecuteCallback_Test8TestBodyEv+0x1d2): error: undefined reference to 'llvm::MCTargetOptions::MCTargetOptions()'
unittests/CodeGen/CGPluginTest/CMakeFiles/CGPluginTest.dir/PluginTest.cpp.o:PluginTest.cpp:function CGPluginTests_ExecuteCallback_Test::TestBody() [clone .localalias]:(.text._ZN34CGPluginTests_ExecuteCallback_Test8TestBodyEv+0x200): error: undefined reference to 'llvm::TargetRegistry::targets()'
unittests/CodeGen/CGPluginTest/CMakeFiles/CGPluginTest.dir/PluginTest.cpp.o:PluginTest.cpp:function CGPluginTests_ExecuteCallback_Test::TestBody() [clone .localalias]:(.text._ZN34CGPluginTests_ExecuteCallback_Test8TestBodyEv+0x3fb): error: undefined reference to 'llvm::Triple::Triple(llvm::Twine const&, llvm::Twine const&, llvm::Twine const&)'
unittests/CodeGen/CGPluginTest/CMakeFiles/CGPluginTest.dir/PluginTest.cpp.o:PluginTest.cpp:function CGPluginTests_ExecuteCallback_Test::TestBody() [clone .localalias]:(.text._ZN34CGPluginTests_ExecuteCallback_Test8TestBodyEv+0x4b4): error: undefined reference to 'llvm::MCContext::MCContext(llvm::Triple const&, llvm::MCAsmInfo const*, llvm::MCRegisterInfo const*, llvm::MCSubtargetInfo const*, llvm::SourceMgr const*, llvm::MCTargetOptions const*, bool, llvm::StringRef)'
unittests/CodeGen/CGPluginTest/CMakeFiles/CGPluginTest.dir/PluginTest.cpp.o:PluginTest.cpp:function CGPluginTests_ExecuteCallback_Test::TestBody() [clone .localalias]:(.text._ZN34CGPluginTests_ExecuteCallback_Test8TestBodyEv+0x4c5): error: undefined reference to 'llvm::MCContext::~MCContext()'
unittests/CodeGen/CGPluginTest/CMakeFiles/CGPluginTest.dir/PluginTest.cpp.o:PluginTest.cpp:function CGPluginTests_ExecuteCallback_Test::TestBody() [clone .localalias]:(.text._ZN34CGPluginTests_ExecuteCallback_Test8TestBodyEv+0x785): error: undefined reference to 'llvm::MCContext::~MCContext()'
unittests/CodeGen/CGPluginTest/CMakeFiles/CGPluginTest.dir/PluginTest.cpp.o:PluginTest.cpp:function CGPluginTests_ExecuteCallback_Test::TestBody() [clone .localalias]:(.text._ZN34CGPluginTests_ExecuteCallback_Test8TestBodyEv+0xb66): error: undefined reference to 'llvm::MCContext::~MCContext()'
collect2: error: ld returned 1 exit status
ninja: build stopped: subcommand failed.

```

</details>

https://github.com/llvm/llvm-project/pull/139059