libxext-dev software package provides X11 miscellaneous extensions library (development headers), you can install in your Ubuntu 14.04 LTS (Trusty Tahr) by running the commands given below on the terminal,
$ sudo apt-get update $ sudo apt-get install libxext-dev
libxext-dev is installed in your system.
Make ensure the libxext-dev package were installed using the commands given below,
$ sudo dpkg-query -l | grep libxext-dev *
You will get with libxext-dev package name, version, architecture and description in a table
| Distro | Ubuntu 14 04 lts trusty tahr |
| Section | Library development |
| Package | libxext-dev |
| Version | 2:1.3.2-1ubuntu0.0.14.04.1 [am |
| Description | X11 miscellaneous extensions library (development headers) |
| Sub Section | libdevel |