rcmd_build_tools: Call R CMD 'command' with build tools active
Description
This is a wrapper around callr::rcmd_safe() that checks
that you have build tools available, and on Windows, automatically sets
the path to include Rtools.
# These env vars are always setcallr::rcmd_safe_env()
if (has_build_tools()) {
rcmd_build_tools("CONFIG", "CC")$stdout
rcmd_build_tools("CC", "--version")$stdout
}