perf tools: Fix build for another rbtree.c change

Fixes:

../../lib/rbtree.c: In function 'rb_insert_color':
../../lib/rbtree.c:95:9: error: 'true' undeclared (first use in this function)
../../lib/rbtree.c:95:9: note: each undeclared identifier is reported only once for each function it appears in
../../lib/rbtree.c: In function '__rb_erase_color':
../../lib/rbtree.c:216:9: error: 'true' undeclared (first use in this function)
../../lib/rbtree.c: In function 'rb_erase':
../../lib/rbtree.c:368:2: error: unknown type name 'bool'
make: *** [util/rbtree.o] Error 1

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: Michel Lespinasse <walken@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-mm@kvack.org
Link: http://lkml.kernel.org/r/50406F60.5040707@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/include/linux/rbtree.h

@@ -1 +1,2 @@
+#include <stdbool.h>
 #include "../../../../include/linux/rbtree.h"