Make sure you have rainbow nest before uppsrc in assembly.
Add "SKELETON" to the main package config.
Add Skeleton package to the project.
"rainbow" is compile time 'interface' that makes possible to replace CtrlCore host platform specific code with something else. Skeleton is this 'something else' that is empty.
'rainbow' works by simple hack: CtrlCore includes "<platform.h>" file. In uppsrc, this file is empty, but in rainbow nest, it contains some defines that change CtrlCore (see rainbow/platform.h and CtrlCore for details).