Fix option type comments for CMDARG_EARLYINIT_FILE and CMDARG_EARLYINIT_COMMAND.

Fix option type comments for CMDARG_EARLYINIT_FILE and CMDARG_EARLYINIT_COMMAND.

The comments in the enum cmdarg_kind were using -sx and -sex instead
of -eix and -eiex.

(Note that gdb --help does not speak about these options).

(pushed as obvious)