Error when installing Watchman on Ubuntu 20.04

Simply install the same watchman 4.9.0 package from official repository by using below commands (and maybe consult with official guide):

sudo add-apt-repository universe
sudo apt-get update
sudo apt-get install watchman

If you are still sure about compilation - install dependencies and then compile the application using commands below:

sudo apt-get install git build-essential libtool libssl-dev pkg-config

cd ~/Downloads
git clone https://github.com/facebook/watchman.git -b v4.9.0 --depth 1
cd watchman
./autogen.sh
./configure --without-python --without-pcre --enable-lenient
make -j$(nproc)
sudo make install