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/util/callchain.c

@@ -20,6 +20,7 @@
 
 #include "asm/bug.h"
 
+#include "debug.h"
 #include "hist.h"
 #include "sort.h"
 #include "machine.h"