Node.js is dependant on some libraries. In your specific case it is very unwise to allow to build node.js with just any compiler - you see, node.js, as any other library-dependant software should be built with same compiler familey, as the libraries it depends on are built. This isn't the strict rule, however - everything may be just OK when using different compiler families. But in many cases the dynamic loader will be unable to resolve specific symbols due to different symbol mangling algorythms (and I, for example, has seens such cases), so unless you made all the needed precautions to exclude this possibility, you probably should not rely on it. So I guess your spec file should be more specific, or may be you should create multiple srpms for cases with different compilers.
P.S. I think this question would better fit to the SE portal.