perf strbuf: Add missing headers

We were only indirectly and by luck getting types, etc needed for this
file, fix it.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-gr8ejvzm7ojk6zwpeplyx9zu@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/strbuf.c

@@ -1,5 +1,5 @@
 #include "debug.h"
-#include "cache.h"
+#include "util.h"
 #include <linux/kernel.h>
 
 int prefixcmp(const char *str, const char *prefix)

tools/perf/util/strbuf.h

@@ -40,6 +40,9 @@
 
 #include <assert.h>
 #include <stdarg.h>
+#include <stddef.h>
+#include <string.h>
+#include <sys/types.h>
 
 extern char strbuf_slopbuf[];
 struct strbuf {