You may be able to install this via package manager, but I built the shared lib from source
sudo apt-get install espeak-ng-espeak
Not sure on the diff, but espeak (no -ng) was available for cygwin package management.
Using it required removing -ng from the link in the g++ command and include in speechsynth.h
When I use it on linux, it has some noise about my sound card printed to stdout/err, but other than that seems to work fine
sudo apt-get install libespeak-dev
sudo apt-get install libncurses5-dev
using makefile for now
make && ./bin/app
or
make && gdb bin/app