parser: use "atom" instead of "sval" in yylval

"sval" is already used for "struct sval".

Signed-off-by: Ran Benita <ran234@gmail.com>
rules: warn when an RMLVO component isn't used

Due to wildcard matches in the rules file, this is only really useful
for misspelled or missing options, e.g.

$ ./test/rmlvo-to-kccgst -o comprose:ralt > /dev/null
xkbcommon: ERROR: Unrecognized RMLVO option "comprose:ralt" was ignored

Although it is more of a warning, it indicates a misconfiguration which
the user probably wants to see. Therefore the log level is ERROR.

Signed-off-by: Ran Benita <ran234@gmail.com>