LLVM can be compiled to JavaScript via Emscripten. It doesn't get much more portable than that. Not to mention a half dozen or so hardware CPU architectures (http://llvm.org/docs/CompilerWriterInfo.html#hardware)
Not sure to what degree we're talking. ARM + x86 has basically everything covered. Even -if- ARM support is bad now, completing it would be easier than creating exactly the custom toolchains that LLVM was designed to abstract away. Who runs browsers on PPC or whatever that isn't consciously taking responsibility for their access to portable software?
http://llvm.org/docs/HowToBuildOnARM.html
i think he means the LLVM bitcode produced.. the IR.
That IR have target processor specifics in it..
but i think the pnacl guys already think about that, and they have a different "bitcode" (as LLVM people say) from the original LLVM..
anyway.. whats more portable than source code? people should stop fancy binary and closed source.. there are no much secrets left these days anyway.. and if you are a hit, nobody can take you that, just by branch the code and call it other name.. unless you are doing something really wrong..