[cfe-dev] Calling the clang-tools-extra source directory 'extra'

[Stephen Kelly via cfe-dev]

Hi,

The buildsystem in clang/tools/CMakeLists.txt currently requires that 
clang-tools-extra, if present, is checked out/cloned to a directory 
called 'extra'.

This is not made clear in the git instructions, so the first thing I've 
always done with a new machine or build is replace that call with a call 
to `add_clang_subdirectory`.

I updated the buildsystem and docs with these proposed commits:

  https://reviews.llvm.org/D52819
  https://reviews.llvm.org/D52820

Any thoughts?

Thanks,

Stephen.