[llvm] Re-apply (#89047):[Exegesis][RISCV] Add RISCV support for llvm-exegesis (PR #120419)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `clang-ppc64le-rhel` running on `ppc64le-clang-rhel-test` while building `llvm` at step 5 "build-unified-tree".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/145/builds/3916

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

```
Step 5 (build-unified-tree) failure: build (failure)
...
92.376 [669/11/5660] Building CXX object lib/Target/RISCV/CMakeFiles/LLVMRISCVCodeGen.dir/GISel/RISCVPostLegalizerCombiner.cpp.o
92.409 [669/10/5661] Building CXX object lib/Target/RISCV/CMakeFiles/LLVMRISCVCodeGen.dir/RISCVISelDAGToDAG.cpp.o
92.430 [669/9/5662] Building CXX object lib/Target/RISCV/CMakeFiles/LLVMRISCVCodeGen.dir/GISel/RISCVInstructionSelector.cpp.o
92.534 [668/9/5663] Linking CXX shared library lib/libLLVMRISCVCodeGen.so.20.0git
92.541 [667/9/5664] Creating library symlink lib/libLLVMRISCVCodeGen.so
101.068 [667/8/5665] Building AMDGPUGenAsmWriter.inc...
102.093 [667/7/5666] Building AMDGPUGenDAGISel.inc...
104.282 [667/6/5667] Building AMDGPUGenAsmMatcher.inc...
104.859 [667/5/5668] Building AMDGPUGenGlobalISel.inc...
105.192 [667/4/5669] Building CXX object tools/llvm-exegesis/lib/RISCV/CMakeFiles/obj.LLVMExegesisRISCV.dir/Target.cpp.o
FAILED: tools/llvm-exegesis/lib/RISCV/CMakeFiles/obj.LLVMExegesisRISCV.dir/Target.cpp.o 
ccache /home/docker/llvm-external-buildbots/clang.17.0.6/bin/clang++ --gcc-toolchain=/gcc-toolchain/usr -DGTEST_HAS_RTTI=0 -DLLVM_BUILD_STATIC -D_DEBUG -D_GLIBCXX_ASSERTIONS -D_GNU_SOURCE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -I/home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-rhel-test/clang-ppc64le-rhel/build/tools/llvm-exegesis/lib/RISCV -I/home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-rhel-test/clang-ppc64le-rhel/llvm-project/llvm/tools/llvm-exegesis/lib/RISCV -I/home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-rhel-test/clang-ppc64le-rhel/build/include -I/home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-rhel-test/clang-ppc64le-rhel/llvm-project/llvm/include -I/home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-rhel-test/clang-ppc64le-rhel/llvm-project/llvm/lib/Target/RISCV -I/home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-rhel-test/clang-ppc64le-rhel/build/lib/Target/RISCV -fPIC -fno-semantic-interposition -fvisibility-inlines-hidden -Werror -Werror=date-time -Werror=unguarded-availability-new -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -pedantic -Wno-long-long -Wc++98-compat-extra-semi -Wimplicit-fallthrough -Wcovered-switch-default -Wno-noexcept-type -Wnon-virtual-dtor -Wdelete-non-virtual-dtor -Wsuggest-override -Wstring-conversion -Wmisleading-indentation -Wctad-maybe-unsupported -fdiagnostics-color -ffunction-sections -fdata-sections -O3 -DNDEBUG -std=c++17  -fno-exceptions -funwind-tables -fno-rtti -UNDEBUG -MD -MT tools/llvm-exegesis/lib/RISCV/CMakeFiles/obj.LLVMExegesisRISCV.dir/Target.cpp.o -MF tools/llvm-exegesis/lib/RISCV/CMakeFiles/obj.LLVMExegesisRISCV.dir/Target.cpp.o.d -o tools/llvm-exegesis/lib/RISCV/CMakeFiles/obj.LLVMExegesisRISCV.dir/Target.cpp.o -c /home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-rhel-test/clang-ppc64le-rhel/llvm-project/llvm/tools/llvm-exegesis/lib/RISCV/Target.cpp
In file included from /home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-rhel-test/clang-ppc64le-rhel/llvm-project/llvm/tools/llvm-exegesis/lib/RISCV/Target.cpp:139:
/home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-rhel-test/clang-ppc64le-rhel/build/lib/Target/RISCV/RISCVGenAsmMatcher.inc:239:19: error: unused function 'MatchRegisterName' [-Werror,-Wunused-function]
  239 | static MCRegister MatchRegisterName(StringRef Name) {
      |                   ^~~~~~~~~~~~~~~~~
/home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-rhel-test/clang-ppc64le-rhel/build/lib/Target/RISCV/RISCVGenAsmMatcher.inc:568:19: error: unused function 'MatchRegisterAltName' [-Werror,-Wunused-function]
  568 | static MCRegister MatchRegisterAltName(StringRef Name) {
      |                   ^~~~~~~~~~~~~~~~~~~~
2 errors generated.
107.912 [667/3/5670] Building AMDGPUGenInstrInfo.inc...
114.389 [667/2/5671] Building AMDGPUGenRegisterBank.inc...
115.039 [667/1/5672] Building AMDGPUGenRegisterInfo.inc...
ninja: build stopped: subcommand failed.

```

</details>

https://github.com/llvm/llvm-project/pull/120419