At the highest level of performance needs, if you want to parallelize the build across machines, you're going to need some kind of storage abstraction for intermediate files since translation units are the easiest place to split builds at.

In some places, where builds are particularly optimized, there are special distributed filesystems just for object files. In this case, it's not necessarily true that the object files are backed by disk even.

Being backed by disk locally mainly helps for incrementally building so that you can change one file and only recompile intermediate files for translation units that depend on this file. Disk/FS caching presumably helps a lot with redundant I/O, and I think most of the benefit of building with tmpfs winds up being putting the source itself in RAM.

Edit: also it's worth noting that many compilers can output object files which can be linked by other linkers, allowing you to mix output from different compilers in some circumstances.