Add support of per file compilation flags (a.k.a. buildoptions) for XCode projects.

[c-smile]

What problem will this solve?

In one of my projects I need to add -fobjc-arc to a group of .mm files. Other files shall stay the same, so I cannot use global settings.

Essentially that is about of fixing this bug: https://github.com/premake/premake-xcode/issues/27

What might be a solution?

Looking for something like this:

filter "files:src/GrMtl**.mm"
    buildoptions { "-fobjc-arc" }

What other alternatives have you already considered?

No other alternative other than applying such settings in XCode manually after project generation.

I can pay for this work. Please contact me.