[R-SIG-Mac] Which version of clang does CRAN's R build use?

[Duncan Murdoch]

The instructions on https://mac.r-project.org/tools/ say to install 
tools using `sudo xcode-select --install`.  Currently for me that installed

   Apple clang version 17.0.0 (clang-1700.0.13.5)

Is that the version of clang that is being used in the CRAN builds?  If 
not, is there an advantage to matching what was used?

Duncan Murdoch