The ground truth of standards

Like any modern libc, LLVM libc also supports a wide number of standards and extensions. To avoid developing headers, wrappers and sources in a disjointed fashion, LLVM libc employs ground truth files. These files live under the spec directory and list ground truth corresponding the ISO C standard, the POSIX extension standard, etc. For example, the path to the ground truth file for the ISO C standard is spec/stdc.td. Tools like the header generator (described in the header generation document), docs generator, etc. use the ground truth files to generate headers, docs etc.