perf sort: Remove needless headers from sort.h, provide fwd struct decls

Reducing the includes hell a bit more, speeding up the build and
avoiding needless rebuilds when just one of those files gets updated.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lkml.kernel.org/n/tip-u63el2vqsovsmnhebx1rcixo@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/ui/stdio/hist.c

@@ -3,6 +3,7 @@
 #include <linux/string.h>
 
 #include "../../util/callchain.h"
+#include "../../util/debug.h"
 #include "../../util/hist.h"
 #include "../../util/map.h"
 #include "../../util/map_groups.h"