From the little info that you give, an educated guess would be that you run a separate install makefile step with the globally installed compiler, while you probably should pass the compiler generated in some previous build step. (PP=c:\fpc\newlygenerated\compiler\ppccrossarmhf or something)
Or it tries to trigger an install without a build (all) step, and then it should be the release compiler (globally installed or manually passed like above)