To solve this error:
rbenv Last 10 log lines: ../.././include/ruby/ruby.h:1755:56: note: expanded from macro 'rb_intern' __extension__ (RUBY_CONST_ID_CACHE((ID), (str)))
Use this command:
CFLAGS="-Wno-error=implicit-function-declaration" RUBY_CONFIGURE_OPTS='--with-readline-dir=/usr/local/opt/readline/' arch -x86_64 rbenv install 2.5.1