Problems with selective file level optimizations and debug symbols on

If you define (for instance) this at the project level

flags { "Symbols" }

But then define this with a filter on specific source files

flags { "Optimize" }
optimize "Speed"

It is possible to see this error when you build in visual studio.

    cl : Command line error D8016: '/ZI' and '/O2' command-line options are incompatible

The bug seems to be the fact that the function m.clCompileFiles does not call m.debugInformationFormat() at the file level if necessary (if optimization is switched on for specific files).