libc: update alarm() implementation to return 0 on error.

This matches the GLibc behaviour, and allows alarm(0xFFFFFFFF) to return 0.

Change-Id: I419aa71b27d6bb2015d15ba6b6112bf62eadcbb8

libc/docs/CHANGES.TXT

@@ -27,6 +27,10 @@ Differences between current and Android 2.2:
 - <unistd.h>: add missing declaration for truncate(). The implementation
   was already here since Android 1.5.
 
+  modify implementation of alarm() to return 0 in case of error (i.e.
+  if a value larger than 0x7fffffff seconds is passed to it). This
+  makes the implementation compliant with the GLibc behaviour.
+
 - <wchar.h>: small fixes to really support wchar_t in Bionic (not there yet).
 
      the size of wchar_t is still 32-bit (decided by the compiler)
@@ -66,6 +70,7 @@ Differences between current and Android 2.2:
 - <sys/vfs.h>: fixed implementation of fstatfs() (also fixes fpathconf()
   which uses it).
 
+
 -------------------------------------------------------------------------------
 Differences between Android 2.2. and Android 2.1:
 

libc/unistd/alarm.c

@@ -51,7 +51,11 @@ alarm(secs)
 	itp->it_value.tv_sec = secs;
 	itp->it_value.tv_usec = 0;
 	if (setitimer(ITIMER_REAL, itp, &oitv) < 0)
+#if 1 /* BIONIC: Same behaviour than GLibc for errors */
+		return 0;
+#else
 		return (-1);
+#endif
 	if (oitv.it_value.tv_usec)
 		oitv.it_value.tv_sec++;
 	return (oitv.it_value.tv_sec);