Check the return value of libc's functions to make `_FORTIFY_SOURCE=2' work.

This fixes bug #24009 reported by Martin Pitt.

* libguile/threads.c (guilify_self_1): Check the return value of
  pipe(2).
  (scm_std_select): Use `full_read ()' instead of `read ()' when reading
  from WAKEUP_FD.

* libguile/async.c (scm_i_queue_async_cell): Use `full_write ()' instead
  of write(2) when writing to SLEEP_FD.

* libguile/fports.c (fport_flush): Likewise.

* libguile/posix.c (getgroups): Use the return value of getgroups(2) as
  NGROUPS.
  (scm_nice): Get the return value of nice(2) to make glibc happy.

* libguile/scmsigs.c (take_signal): Use `full_write ()' instead of
  write(2).

libguile/async.c

@@ -1,4 +1,4 @@
-/* Copyright (C) 1995,1996,1997,1998,2000,2001, 2002, 2004, 2006 Free Software Foundation, Inc.
+/* Copyright (C) 1995,1996,1997,1998,2000,2001, 2002, 2004, 2006, 2008 Free Software Foundation, Inc.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
@@ -41,6 +41,8 @@
 #include <unistd.h>
 #endif
 
+#include <full-write.h>
+
 
 /* {Asynchronous Events}
  *
@@ -241,13 +243,13 @@ scm_i_queue_async_cell (SCM c, scm_i_thread *t)
   if (sleep_fd >= 0)
     {
       char dummy = 0;
+
       /* Likewise, T might already been done with sleeping here, but
 	 interrupting it once too often does no harm.  T might also
 	 not yet have started sleeping, but this is no problem either
 	 since the data written to a pipe will not be lost, unlike a
-	 condition variable signal.
-      */
-      write (sleep_fd, &dummy, 1);
+	 condition variable signal.  */
+      full_write (sleep_fd, &dummy, 1);
     }
 
   /* This is needed to protect sleep_mutex.