perf tools: Use just forward declarations for struct thread where possible

Removing various instances of unnecessary includes, reducing the maze of
header dependencies.

Link: http://lkml.kernel.org/n/tip-hwu6eyuok9pc57alookyzmsf@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-c2c.c

@@ -32,6 +32,7 @@
 #include <asm/bug.h>
 #include "ui/browsers/hists.h"
 #include "evlist.h"
+#include "thread.h"
 
 struct c2c_hists {
 	struct hists		hists;