eclipse: c/c++ build / builder settings page is disabled (grey), can't change settings

The problem is actual on windows and appears when you using toolchains. I found small hack to correct it.

you can only customize the builder settings if you choose an empty makefile project.

delete the project, keeping the contents on the disk. then click file -> new -> c++ project. instead of choosing "empty project" under "executable", choose "empty project" under "makefile project".