To install watchman on Fedora 28, these are all the hoops I had to jump through.

install-watchman.sh

# The following packages are needed during `make`
#  - openssl-devel so you don't get:
#      ContentHash.cpp:13:10: fatal error: openssl/sha.h: No such file or directory
#  - redhat-rpm-config so you don't get:
#      gcc: error: /usr/lib/rpm/redhat/redhat-hardened-cc1: No such file or directory
#  - python-devel so you don't get:
#      pywatchman/bser.c:31:10: fatal error: Python.h: No such file or directory
sudo dnf install openssl-devel redhat-rpm-config python-devel libtool

# The rest is just instructions from
# https://codeyarns.com/2015/02/10/how-to-install-and-use-watchman/
git clone https://github.com/facebook/watchman.git ~/git/facebook/watchman
cd ~/git/facebook/watchman
./autogen.sh
./configure --enable-lenient
make
sudo make install

sudo bash -c 'echo 524288 > /proc/sys/fs/inotify/max_user_watches'
sudo bash -c 'echo 524288 > /proc/sys/fs/inotify/max_queued_events'
sudo bash -c 'echo 524288 > /proc/sys/fs/inotify/max_user_instances'
watchman shutdown-server

I also stumbled across build errors - ./configure --enable-lenient fixed it for me! (using Fedora 31)