[Libc] fix issue with undefined extern; restore GCC test with linking

headers/header_spec.txt

@@ -296,6 +296,7 @@ share/libc/termios.h: CEA_LGPL
 share/libc/tgmath.h: CEA_LGPL
 share/libc/time.c: CEA_LGPL
 share/libc/time.h: CEA_LGPL
+share/libc/unistd.c: CEA_LGPL
 share/libc/unistd.h: CEA_LGPL
 share/libc/utime.h: CEA_LGPL
 share/libc/utmpx.h: CEA_LGPL

share/libc/__fc_runtime.c

@@ -35,4 +35,5 @@
 #include "stdio.c"
 #include "stdlib.c"
 #include "string.c"
+#include "unistd.c"
 #include "wchar.c"

share/libc/unistd.c

+/**************************************************************************/
+/*                                                                        */
+/*  This file is part of Frama-C.                                         */
+/*                                                                        */
+/*  Copyright (C) 2007-2019                                               */
+/*    CEA (Commissariat à l'énergie atomique et aux énergies              */
+/*         alternatives)                                                  */
+/*                                                                        */
+/*  you can redistribute it and/or modify it under the terms of the GNU   */
+/*  Lesser General Public License as published by the Free Software       */
+/*  Foundation, version 2.1.                                              */
+/*                                                                        */
+/*  It is distributed in the hope that it will be useful,                 */
+/*  but WITHOUT ANY WARRANTY; without even the implied warranty of        */
+/*  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the         */
+/*  GNU Lesser General Public License for more details.                   */
+/*                                                                        */
+/*  See the GNU Lesser General Public License version 2.1                 */
+/*  for more details (enclosed in the file licenses/LGPLv2.1).            */
+/*                                                                        */
+/**************************************************************************/
+
+#include "unistd.h"
+#include "__fc_builtin.h"
+__PUSH_FC_STDLIB
+
+volatile char __fc_ttyname[TTY_NAME_MAX];
+__POP_FC_STDLIB

tests/libc/oracle/fc_libc.0.res.oracle

@@ -157,12 +157,12 @@
    wcstombs (0 call); wctomb (0 call); wmemchr (0 call); wmemcmp (0 call);
    wmemmove (0 call); write (0 call); 
   
-  'Extern' global variables (17)
+  'Extern' global variables (16)
   ==============================
    __fc_basename; __fc_dirname; __fc_getpwuid_pw_dir; __fc_getpwuid_pw_name;
    __fc_getpwuid_pw_passwd; __fc_getpwuid_pw_shell; __fc_hostname; __fc_locale;
-   __fc_locale_names; __fc_mblen_state; __fc_mbtowc_state; __fc_ttyname;
-   __fc_wctomb_state; optarg; opterr; optopt; tzname
+   __fc_locale_names; __fc_mblen_state; __fc_mbtowc_state; __fc_wctomb_state;
+   optarg; opterr; optopt; tzname
   
   Potential entry points (1)
   ==========================
@@ -242,6 +242,7 @@
 #include "syslog.h"
 #include "termios.h"
 #include "time.h"
+#include "unistd.c"
 #include "unistd.h"
 #include "wchar.c"
 #include "wchar.h"

tests/libc/oracle/fc_libc.1.res.oracle

@@ -1742,8 +1742,7 @@ extern void sync(void);
     assigns \result \from (indirect: name); */
 extern long sysconf(int name);
 
-extern char volatile __fc_ttyname[32];
-
+char volatile __fc_ttyname[32];
 char volatile *__fc_p_ttyname = __fc_ttyname;
 /*@ requires valid_fildes: 0 ≤ fildes < 1024;
     ensures

tests/libc/runtime.c

 /* run.config*
    COMMENT: tests that the runtime can compile without errors (for PathCrawler, E-ACSL, ...)
-   CMD: gcc -fsyntax-only -D__FC_MACHDEP_X86_64 share/libc/__fc_runtime.c -Wno-attributes -std=c99
+   CMD: gcc -D__FC_MACHDEP_X86_64 share/libc/__fc_runtime.c -Wno-attributes -std=c99 -o /dev/null
    OPT:
  */