libc: Implement time() using clock_gettime().

The cool POSIX kids use clock_gettime() now because it has NANOSECONDS (and different clocks!),
but ANSI C prefers this function.

We can still implement it based on clock_gettime(), we just have to discard the NANOSECONDS.

apps/app.c

@@ -16,9 +16,8 @@ int main()
 
     console_print(buffer);
 
-    struct timespec ts;
-    clock_gettime(CLOCK_REALTIME, &ts);
-    snprintf(buffer, sizeof(buffer), "Realtime clock: %ld s, %ld ns\n", ts.tv_sec, ts.tv_nsec);
+    time_t now = time(NULL);
+    snprintf(buffer, sizeof(buffer), "Realtime clock: %ld s\n", now);
 
     console_print(buffer);
 

libc/include/time.h

@@ -12,6 +12,9 @@ extern "C"
     /* Get the current value of a system clock. */
     int clock_gettime(clockid_t id, struct timespec* ts);
 
+    /* Get the current wall clock time. */
+    time_t time(time_t* tp);
+
 #ifdef __cplusplus
 }
 #endif

libc/src/time.cpp

@@ -10,4 +10,14 @@ extern "C"
         long rc = syscall(SYS_clock_gettime, id, ts);
         __errno_return(rc, int);
     }
+
+    time_t time(time_t* tp)
+    {
+        struct timespec ts;
+        if (clock_gettime(CLOCK_REALTIME, &ts) < 0) return (time_t)-1;
+
+        if (tp) *tp = ts.tv_sec;
+
+        return ts.tv_sec;
+    }
 }