doc: another case of the RTF backend corrupting state
doc: another case of the RTF backend corrupting state

Another case of the RTF backend corrupting global state.  "Fix" it by
only outputting one format at a time; this also makes it possible to
run in parallel.

letolabs/nasm,turingstudio/nasm,techkey/nasm,letolabs/nasm,techkey/nasm,projedi/nasm,letolabs/nasm,projedi/nasm,Distrotech/nasm,Distrotech/nasm,projedi/nasm,Distrotech/nasm,Distrotech/nasm,techkey/nasm,techkey/nasm,turingstudio/nasm,techkey/nasm,projedi/nasm,turingstudio/nasm,projedi/nasm,turingstudio/nasm