To install watchman on Fedora 26, these are all the hoops I had to jump through.

install-watchman.bash

# 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

# 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
cd watchman
./autogen.sh
./configure
make
sudo make install

well I installed those two groups and I'm still getting the same error.

I'm taking my issue here: facebook/watchman#607

libssl-dev solution working and i also installed libcrypto++-dev package.After that, i did ./autogen.sh , ./configure and make again.

For apt (Ubuntu, Debian…):

sudo apt-get install python-dev   # for python2.x installs
sudo apt-get install python3-dev  # for python3.x installs

For yum (CentOS, RHEL…):

sudo yum install python-devel   # for python2.x installs
sudo yum install python34-devel   # for python3.4 installs

For dnf (Fedora…):

sudo dnf install python2-devel  # for python2.x installs
sudo dnf install python3-devel  # for python3.x installs

For zypper (openSUSE…):

sudo zypper in python-devel   # for python2.x installs
sudo zypper in python3-devel  # for python3.x installs

Repeat this following action
$ ./configure
$ make
$ sudo make install

Source

for centos:
yum groupinstall "Development Tools"
yum install libtool
yum install openssl-devel redhat-rpm-config python-devel