perf tools: No need to include namespaces.h in util.h

The only thing that is needed there is a forward declaration for 'struct
nsinfo', so disentanble this, which in turns allows built-in clang
builds, i.e. 'make LIBCLANGLLVM=1 -C tools/perf'.

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: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Cc: Sandipan Das <sandipan@linux.vnet.ibm.com>
Cc: Wang Nan <wangnan0@huawei.com>
Link: https://lkml.kernel.org/n/tip-vq26rsuwq1cqylpcyvq89c84@git.kernel.orgSigned-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/util.h

@@ -11,8 +11,7 @@
 #include <stdlib.h>
 #include <stdarg.h>
 #include <linux/compiler.h>
-#include <linux/types.h>
-#include "namespaces.h"
+#include <sys/types.h>
 
 /* General helper functions */
 void usage(const char *err) __noreturn;
@@ -26,6 +25,7 @@ static inline void *zalloc(size_t size)
 #define zfree(ptr) ({ free(*ptr); *ptr = NULL; })
 
 struct dirent;
+struct nsinfo;
 struct strlist;
 
 int mkdir_p(char *path, mode_t mode);