kallsyms: unbreak kallmodsyms after CONFIG_KALLMODSYMS addition

kallsyms: unbreak kallmodsyms after CONFIG_KALLMODSYMS addition

The recent addition of CONFIG_KALLMODSYMS In 28df3b99a7 had the effect
of entirely disabling all module info in /proc/kallmodsyms, thus
breaking all module-specific symbol lookups from DTrace.

This is because you can't use a CONFIG_ symbol in a HOSTCC-compiled
program without including autoconf.h by hand, and we weren't, so
scripts/kallsyms.c always acted as if CONFIG_KALLMODSYMS was turned
off and didn't populate the kallsyms_modules or kallsyms_symbol_modules
tables.

(Including autoconf.h in this context is safe, because kallsyms.c never
gets compiled until after some *config target has run.  Other build
tools in a similar position, such as modpost, already do this.)

Orabug: 21539840
Signed-off-by: Nick Alcock <nick.alcock@oracle.com>
Acked-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>
Acked-by: Kris Van Hees <kris.van.hees@oracle.com>