There’s two project settings problems with current tip when trying to build RTAS plugins.
One problem affects users of XCode 4.3 and causes a compilation error:
.../ASConnUtil.h:25:10: fatal error: 'Components.h' file not found
The other problem affects people who use a relative path for their RTAS SDK and causes a linking error. libPluginLibrary.a can’t be found.
This is due to XCodeProjectExporter::getLinkerFlagsForStaticLibrary doing
if (! library.isAbsolute()) searchPath = "$(SRCROOT)/" + searchPath;
while the code defining SRCROOT was removed at commit ead42bd39acda45e3ccca0e14070cd714e27e5a8
one possible fix is re-adding those lines defining SRCROOT.