Outputing the predefined variables `make -R` references?

Question

According to the docs on make there is a -R switch,

-R, --no-builtin-variables
            Don't define any built-in variables.

How can I find those builtin variables and their values?

Answer 1

I think this is the closest you can get

env -i make -rp | grep -v '^#' | grep ' = '

That prints out the database less the rules, in an environment that isn't pristine result in what I believe is just the builtin variables.