Dica testada no Devuan Ascii (Debian Stretch).

Ao tentar compilar o Polybar, me deparava com o erro:

--   No package 'xcb-composite' found
CMake Error at /usr/share/cmake-3.7/Modules/FindPkgConfig.cmake:415 (message):
  A required package was not found
Call Stack (most recent call first):
  /usr/share/cmake-3.7/Modules/FindPkgConfig.cmake:588 (_pkg_check_modules_internal)
  cmake/common/utils.cmake:95 (pkg_check_modules)
  cmake/03-libs.cmake:20 (querylib)
  CMakeLists.txt:34 (include)

-- Configuring incomplete, errors occurred!
See also "/home/xerxeslins/polybar/build/CMakeFiles/CMakeOutput.log".
See also "/home/xerxeslins/polybar/build/CMakeFiles/CMakeError.log".
** Failed to generate build... read output to get a hint of what went wrong

Faltando "xcb-composite"? Mas ele estava instalado pelo pacote "libxcb-composite0"! Então descobri que era o pacote "libxcb-composite0-dev" que deveria ser instalado.

Então, em resumo, a compilação do Polybar ficou assim:

Instalação de dependências:

# apt-get install cmake cmake-data libcairo2-dev libxcb1-dev libxcb-ewmh-dev libxcb-icccm4-dev libxcb-image0-dev libxcb-randr0-dev libxcb-util0-dev libxcb-xkb-dev pkg-config python-xcbgen xcb-proto libxcb-xrm-dev i3-wm libasound2-dev libmpdclient-dev libiw-dev libcurl4-openssl-dev libpulse-dev libxcb-composite0-dev

Clone:

git clone https://github.com/jaagr/polybar.git

E build:

cd polybar && ./build.sh

É isso.