Unable to install gem

[mikehale]

I tried to install this ruby gem with libssh 0.8.7 on my system, but I'm seeing this error. Any ideas?

checking for libssh/libssh.h... yes
checking for -lssh... yes
checking for -lssh_threads... no
Cannot find libssh_threads
*** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of necessary
libraries and/or headers.  Check the mkmf.log file for more details.  You may
need configuration options.

Provided configuration options:
        --with-opt-dir
        --without-opt-dir
        --with-opt-include
        --without-opt-include=${opt-dir}/include
        --with-opt-lib
        --without-opt-lib=${opt-dir}/lib
        --with-make-prog
        --without-make-prog
        --srcdir=.
        --curdir
        --ruby=/Users/mhale/.rbenv/versions/2.6.2/bin/$(RUBY_BASE_NAME)
        --with-sshlib
        --without-sshlib
        --with-ssh_threadslib
        --without-ssh_threadslib