`includedirsafter` on xcode4

[Jarod42]

What seems to be the problem? xcode4 doesn't fully support (new feature added by #2028) includedirsafter. (i.e it adds them as symtem/external includes)

What did you expect to happen? pass to gcc/clang the -idirafter flags to the directories

How can we reproduce this? With testing project project-includedirsafter.

• [ ] Visual Studio 2022 (vs2022)
• [ ] Visual Studio 2019 (vs2019)
• [ ] Visual Studio 2017 (vs2017)
• [ ] Visual Studio 2015 (vs2015)
• [ ] Visual Studio 2012 (vs2012)
• [ ] Visual Studio 2010 (vs2010)
• [ ] Visual Studio 2008 (vs2008)
• [ ] Visual Studio 2005 (vs2005)
• [ ] GNU Makefile (gmake)
• [ ] GNU Makefile 2 (gmake2)
• [x] XCode (xcode)
• [ ] Codelite
• [ ] Other (Please list below)

What version of Premake are you using? master branch

Anything else we should know? Instead of adding includedirsafter in system/external include dirs fields, adding toolset.getincludedirs(cfg, {}, {}, cfg.frameworkdirs, cfg.includedirsafter) as build option should do the job.