Undefined symbol: llvm::XCoreMCRegisterClassStorage building clang

Build:
```
cmake -S llvm -B build -G Ninja -DLLVM_ENABLE_PROJECTS="clang" -DCMAKE_BUILD_TYPE=Debug -DLLVM_PARALLEL_LINK_JOBS=1 -DLLVM_PARALLEL_COMPILE_JOBS=6 -DLLVM_ENABLE_LLD=ON -DBUILD_SHARED_LIBS=ON
cd build
ninja clang
```

Error message:
FAILED: lib/libLLVMXCoreDisassembler.so
ld.lld: error: undefined symbol: llvm::XCoreMCRegisterClassStorage

Run the supplied CMake and Ninja commands first to reproduce the failure. Then trace the XCore disassembler target and the definition and use of llvm::XCoreMCRegisterClassStorage; done means lib/libLLVMXCoreDisassembler.so links successfully and ninja clang completes.

Written by the indexing model from the issue text.