kconfig: warn of unhandled characters in Kconfig commands

In Kconfig, definitions of options take the following form:
"<COMMAND> <PARAM> <PARAM> ...". COMMANDs and PARAMs are treated
slightly different by the underlying parser.

While commit 2e0d737fc7 ("kconfig: don't silently ignore unhandled
characters") introduced a warning for unsupported characters around
PARAMs, it does not cover situations where a COMMAND has additional
characters before it.

This change makes Kconfig emit a warning if superfluous characters
are found before COMMANDs. As the 'help' statement sometimes is
written as '---help---', the '-' character would now also be regarded
as unhandled and generate a warning. To avoid that, '-' is added to
the list of allowed characters, and the token '---help---' is included
in the zconf.gperf file.

Reported-by: Valentin Rothberg <valentinrothberg@gmail.com>
Signed-off-by: Andreas Ruprecht <andreas.ruprecht@fau.de>
Reviewed-by: Ulf Magnusson <ulfalizer@gmail.com>
Tested-by: Ulf Magnusson <ulfalizer@gmail.com>
Signed-off-by: Michal Marek <mmarek@suse.com>

scripts/kconfig/zconf.gperf

@@ -22,6 +22,7 @@ comment,	T_COMMENT,	TF_COMMAND
 config,		T_CONFIG,	TF_COMMAND
 menuconfig,	T_MENUCONFIG,	TF_COMMAND
 help,		T_HELP,		TF_COMMAND
+---help---,	T_HELP,		TF_COMMAND
 if,		T_IF,		TF_COMMAND|TF_PARAM
 endif,		T_ENDIF,	TF_COMMAND
 depends,	T_DEPENDS,	TF_COMMAND