Files with individual build settings are not tagged in the project explorer, There is no way to identify them. I think I have seen that they are tagged in an older release. Otherwise treat this report as a feature request.
GNU ARM C/C++ Development Support 0.5.3.201007072245 org.eclipse.cdt.cross.arm.gnu.feature.group
Eclipse IDE for C/C++ Developers 188.8.131.5200617-0520 epp.package.cpp