It's right. Seems we talk about the same thing. Summary:

• Plugin don't need in #ifdef to compile-time disabling, because...
• Plugin available and can be used at all platforms.
• Path to pkgconfig executable and environment vars are configurable from kdevelop settings menu.

Pkgconfig available at Windows and Mac, but not installed by default and have no a standart place. On Windows pkgconfig may be in MinGW or Cygwin installations, on Mac in macports or in homebrew for example. It's depends from user configuration and wishes. So this functionality is optional and high specialized, but functionality of common-definesandincludes is common and generic. In most cases user cannot disable common-definesandincludes because it's a dependency for cmakebuilder, makebuilder and some other significant plugins.

You'll get more feedback on this when you present your patch via a differential (aka "patch") review.

Already https://phabricator.kde.org/D17794
Sorry, it was my misunderstanding. May i suggest to add link to these instructions to this page :)

This plugin may be useful for any c/c++ project. For example indexer for CMake project KDevelop (sources of ide) don't see all required includes for me. I've added paths to includes of QT, KDE and some other manually. And it was much easier than trying to fix automation.

Fix typo