When -fcf-protection=branch is used, the compiler will generate jump
tables for switch statements where the indirect jump is prefixed with
the NOTRACK prefix, so it can jump to non-ENDBR targets. Since the
indirect jump targets are generated by the compiler and stored in
read-only memory, this does not result in a direct loss of hardening.
But if the jump table index is attacker-controlled, the indirect jump
may not be constrained by CET.
Document -mcet-switch to generate jump tables for switch statements with
ENDBR and skip the NOTRACK prefix for indirect jump. This option should
be used when the NOTRACK prefix is disabled.