System requirements: COIN-OR Clp (>= 1.16) with development headers, and
a C++17 compiler. Debian/Ubuntu: coinor-libclp-dev, Fedora:
coin-or-Clp-devel, macOS: brew install clp, Windows: supplied
by Rtools (4.3 or later). CLP_CFLAGS and CLP_LIBS point the
build at an installation elsewhere.