ninja docs-clang-html fails with tools/clang/docs/ClangCommandLineReference.rst:22:Duplicate explicit target name: "cmdoption-clang--prefix".

Hi,

Since I’ve migrated to a newer linux distro I can’t build docs-clang-html.

  1. get LLVM
  2. cmake -GNinja -DLLVM_ENABLE_SPHINX=YES -DSPHINX_OUTPUT_HTML=YES -DLLVM_BUILD_DOCS=YES ~/llvm
  3. ninja docs-clang-html

As a workaround, you can set SPHINX_WARNINGS_AS_ERRORS=OFF.