Plan 9 refreshingly evicted this nonsense from the native compilers (mostly) and the code base.[1]
Yes, You can write portable code without #ifdef, configure scripts, and libtool. Plan 9 shows how.
Some people get upset at mentions of Plan 9, however, so for a more current example, the Go source tree is a good reference. There's no cpp in Go, thank goodness, and they've shown superior portability to systems that revolve around #ifdef.
ron