[clang][doc] Re-generation of DiagnosticsReference.rst
I was looking around in clang to understand how diagnostics are implemented when I figured out that the last time DiagnosticsReference.rst got generated was on Oct 26, 2017 .
It has been hand-tailored since then.
The listed diagnostics and those that are actually known by clang have significantly diverged.
The diff is ~490KB.
I managed to re-generate the file with the following command:
llvm-project/clang/include/clang/Basic$ ../../../../build/bin/clang-tblgen --gen-diag-docs Diagnostic.td > ../../../docs/DiagnosticsReference.rst