This folder contains the various required libraries for QGC to compile. They are distributed with the codebase to ease development.
Qt Widgets for Technical Applications
Version: 6.1
Source obtained: svn checkout svn://svn.code.sf.net/p/qwt/code/branches/qwt-6.1 qwt
Contents of /libs/qwt is the contents of the /src directory from the Qwt repository.
qwt.pri file is custom made to compile all necessary Qwt code in with QGC.