--with-gmp is not working at all because HAVE_GMP_H was missing since 18eaf0be90. [Bug #20515] bug: https://bugs.ruby-lang.org/issues/20515 follow-up: https://bugs.ruby-lang.org/issues/20494 follow-up: 18eaf0be90 follow-up: https://github.com/ruby/ruby/pull/10805
18eaf0be90