sys/time.h: Fix timersub macro; time_t is unsigned

ChangeLog

@@ -11263,3 +11263,4 @@
 	  struct sigevent.  This initial implementation will only work in the
 	  FLAT build.  See the top-level TODO file for additional details
 	  (2015-12-30).
+

include/pthread.h

@@ -50,7 +50,7 @@
 #include <stdbool.h>        /* C99 boolean types */
 #include <unistd.h>         /* For getpid */
 #include <semaphore.h>      /* Needed for sem_t */
-#include <signal.h>         /* Needed for sigset_t */
+#include <signal.h>         /* Needed for sigset_t, includes this file */
 #include <time.h>           /* Needed for struct timespec */
 
 /********************************************************************************
@@ -441,8 +441,8 @@ int pthread_sigmask(int how, FAR const sigset_t *set, FAR sigset_t *oset);
 #include <sys/types.h>
 #include <stdbool.h>
 
-/* Avoid a circular dependencies by assuring that simple type definitions
- * are avaiable in any inclusion ordering.
+/* Avoid circular dependencies by assuring that simple type definitions are
+ * available in any inclusion ordering.
  */
 
 #ifndef __PTHREAD_KEY_T_DEFINED

include/signal.h

@@ -45,8 +45,9 @@
 
 #include <stdint.h>
 #include <time.h>
+
 #ifdef CONFIG_SIG_EVTHREAD
-#  include <pthread.h>  /* Needed for pthread_attr_t */
+#  include <pthread.h>  /* Needed for pthread_attr_t, includes this file */
 #endif
 
 /********************************************************************************
@@ -320,8 +321,8 @@ int sigqueue(int pid, int signo, FAR void *sival_ptr);
 
 #include <stdint.h>
 
-/* Avoid a circular dependencies by assuring that simple type definitions
- * are avaiable in any inclusion ordering.
+/* Avoid circular dependencies by assuring that simple type definitions are
+ * available in any inclusion ordering.
  */
 
 #ifndef __SIGSET_T_DEFINED

include/sys/time.h

@@ -78,12 +78,12 @@
   do \
     { \
       (vvp)->tv_sec = (tvp)->tv_sec - (uvp)->tv_sec; \
-      (vvp)->tv_usec = (tvp)->tv_usec - (uvp)->tv_usec; \
-      if ((vvp)->tv_usec < 0) \
+      if ((uvp)->tv_usec > (tvp)->tv_usec) \
         { \
           (vvp)->tv_sec--; \
-          (vvp)->tv_usec += 1000000; \
+          (tvp)->tv_usec += 1000000; \
         } \
+      (vvp)->tv_usec = (tvp)->tv_usec - (uvp)->tv_usec; \
     } \
   while (0)