update build infrastructure for llvm-16.0.6

Update build infrastructure for LLVM 13.0.0.

regen llvm man pages from rst with

cd /usr/src/gnu/llvm/llvm/docs
gmake -f Makefile.sphinx man

cd /usr/src/gnu/llvm/clang/docs
gmake -f Makefile.sphinx man

cmake -DLLVM_ENABLE_SPHINX=ON -DLLDB_INC

regen llvm man pages from rst with

cd /usr/src/gnu/llvm/llvm/docs
gmake -f Makefile.sphinx man

cd /usr/src/gnu/llvm/clang/docs
gmake -f Makefile.sphinx man

cmake -DLLVM_ENABLE_SPHINX=ON -DLLDB_INCLUDE_TESTS=OFF /usr/src/gnu/llvm/lldb/
make docs-lldb-man

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Update clang build infrastructure for LLVM 8.0.0.

add llvm-config.1 from llvm-config.rst

Generated with gmake and py-sphinx installed via
cd /usr/src/gnu/llvm/docs && gmake -f Makefile.sphinx man