missing_threads.h: threads.h exists since glibc-2.28

src/basic/process-util.c

@@ -15,6 +15,7 @@
 #include <sys/types.h>
 #include <sys/wait.h>
 #include <syslog.h>
+#include <threads.h>
 #include <unistd.h>
 #if HAVE_VALGRIND_VALGRIND_H
 #include <valgrind/valgrind.h>
@@ -43,7 +44,6 @@
 #include "memory-util.h"
 #include "missing_sched.h"
 #include "missing_syscall.h"
-#include "missing_threads.h"
 #include "mountpoint-util.h"
 #include "namespace-util.h"
 #include "nulstr-util.h"