[BOLT][Instrumentation] Disallow combining append-pid with sleep-time/wait-forks

The point of instrumentation-sleep-time option is to have a watcher
process which shares memory with all other forks and dumps a common
profile each n seconds. Combining it with append-pid suggests that we
should get a private profile of each fork every n seconds, but such
behavior is not implemented currently and is not easy to implement in
general, because we somehow need to intercept each individual fork,
launch a watcher process just for that fork, and also map counters so
that they're only shared with that single fork. Since we're not doing
it, we just disallow such combination of options.

Reviewed By: rafauler, Amir
Differential Revision: https://reviews.llvm.org/D153771