Can anyone tell me how to compile the Clang compiler into LLVM bytecode (that is, self-host Clang)? The reason I want to do this is so that I can take the resulting LLVM bytecode and then use Emscripten to produce a C to Javascript compiler.
You can get clang to output into LLVM bytecode by using the -emit-llvm command-line flag, along with the -c flag. (If you use the -S flag instead of -c, you get a textual representation of the LLVM bytecode.) You don't need to compile clang into LLVM bytecode for that to work.
If you want to try to run clang itself inside a browser, then you will need to compile all of clang into LLVM bytecode, and then link the object files together using llvm-link. Then you'll need to figure out how to give the compiled compiler access to the system header files it needs. I don't know if there is a build option for all that, but I haven't ever seen anything in the ./configure options for that, so I suspect not. But it's possible that it exists.