4.0.0

For all it is worth,

homebrew upgraded R to 4.0.0 on Catalina and I did notice that homebrew
asked for an XCode Command Line Tools upgrade

I then sourced as usual my package.R which installs the ones I use, and
it did install a number of packages from source (which I assusme is
becasue they haven't yet loaded as binary packages).

No drama whatsoever. In particular a complicated :yX report with knitR 
produces the expected result :-)-O

el

Running R 3.6 has been working fine. I just upgraded to R 4.0 and I cannot
build packages from source. I have tried the following:

1. Installed R 4.0 binary on my mac (macOS 10.14.6). Installation went
fine, but when I try to build packages from source I get errors like this:

[...]