Fix a missing config.h dependency when building sparseset.o to prevent
"conflicting types for 'strsignal'" error, which can intermittently crop
up for high values of make -j.
Thanks to Richard Purdie and Jeff Dike for their help in tracking this
down.
Signed-off-by: Scott Garman <scott.a.garman@intel.com>
Signed-off-by: Richard Purdie <rpurdie@linux.intel.com>