This blog is updated daily.
A general description is here.
Where recorded at installation, ‘R CMD check’ reports the C and Fortran compilers used to build R.
It reports the OS in use (if known, as given by ‘osVersion’) as well as that R was built for.
It notes if a C++ standard was specified which is older than the current default: many packages have used C++11 to mean ‘not C++98’ - as C++11 is the minimum supported since R 4.0.0, that specification can probably be removed.
‘R CMD INSTALL’ reports the compilers (and on macOS, the SDK) used, and this is copied to the output of ‘R CMD check’.
Where a C++ standard is specified, it is reported.