Sure, if you are stuck with GCC, and have no plans to move, it makes sense to improve GCC's preprocessor for a number of reasons (warp produces cacheable artifacts, etc).
But it's actually not that tricky, since you can just change the defines it makes (after all, if you are maintaining your own toolchain, you are maintaining your own toolchain).
In fact, you are already doing it with warp to emulate GCC's defines.
Suffice to say, we've done it before to provide clang diagnostics but build with GCC.
Yes, and no offense, but while other large companies have folks working on fixing this in public, i don't see facebook trying.
This is really not meant as a dig (really!), but more of "why i figured facebook was not trying to make a transition". The companies trying to do so, are contributing heavily to LLVM to make that transition :)
But it's actually not that tricky, since you can just change the defines it makes (after all, if you are maintaining your own toolchain, you are maintaining your own toolchain).
In fact, you are already doing it with warp to emulate GCC's defines.
Suffice to say, we've done it before to provide clang diagnostics but build with GCC.