Adds a new option -disable_rseq, which returns -ENOSYS on any SYS_rseq system call. This is intended as a workaround for applications that do not satisfy DR's limitations for full rseq support.
Adds a test that fails unless -disable_rseq is passed.
Moves the rseq limitations list to a new section on rseq in the documentation.
Issue: #2350 (closed)