GNU make and a C++ compiler are always available, because
make and gcc are dependencies of base-devel.
The ignored values "C++11", "C++17" and "GNU make" indicate
build-time dependencies only.
- Remove unnecessary `{}` around `_pkgname` in the url
- Remove unnecessary `-p` option to `mkdir`
- Use standard argument order for `R CMD INSTALL` by putting
options before positional arguments