Use weak symbols for sudo_warn_gettext() and sudo_warn_strerror()

so distros using "-Wl,--no-undefined" in LDFLAGS don't run into
problems.

lib/util/locale_weak.c

@@ -0,0 +1,80 @@
+/*
+ * Copyright (c) 2013-2015 Todd C. Miller <Todd.Miller@courtesan.com>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include <config.h>
+
+#include <sys/types.h>
+
+#ifdef HAVE_SYS_WEAK_ALIAS
+
+#include <stdio.h>
+#include <stdlib.h>
+#ifdef HAVE_STRING_H
+# include <string.h>
+#endif /* HAVE_STRING_H */
+#ifdef HAVE_STRINGS_H
+# include <strings.h>
+#endif /* HAVE_STRINGS_H */
+
+#define DEFAULT_TEXT_DOMAIN	"sudo"
+#include "sudo_gettext.h"	/* must be included before sudo_compat.h */
+
+#include "sudo_compat.h"
+#include "sudo_fatal.h"
+
+/*
+ * Weak symbols for sudo_warn_gettext_v1() and sudo_warn_strerror_v1().
+ * These stubs are provided to make libsudo_util link with no undefined
+ * symbols.
+ */
+
+# ifdef HAVE_LIBINTL_H
+/* We only need to swap locales in the plugin. */
+char *
+sudo_warn_gettext_weak(const char *msgid)
+{
+    return gettext(msgid);
+}
+#  if defined(HAVE_SYS_WEAK_ALIAS_ATTRIBUTE)
+char *sudo_warn_gettext_v1(const char *msgid)
+    __attribute__((weak, alias("sudo_warn_gettext_weak")));
+#  elif defined(HAVE_SYS_WEAK_ALIAS_PRAGMA)
+#   pragma weak sudo_warn_gettext_v1 = sudo_warn_gettext_weak
+#  elif defined(HAVE_SYS_WEAK_ALIAS_HPSECONDARY)
+#   pragma _HP_SECONDARY_DEF sudo_warn_gettext_weak sudo_warn_gettext_v1
+#  elif defined(HAVE_SYS_WEAK_ALIAS_CRIDUPLICATE)
+#   pragma _CRI duplicate sudo_warn_gettext_v1 as sudo_warn_gettext_weak
+#  endif
+# endif /* HAVE_LIBINTL_H */
+
+/* We only need to swap locales in the plugin. */
+char *
+sudo_warn_strerror_weak(int errnum)
+{
+    return strerror(errnum);
+}
+# if defined(HAVE_SYS_WEAK_ALIAS_ATTRIBUTE)
+char *sudo_warn_strerror_v1(int errnum)
+    __attribute__((weak, alias("sudo_warn_strerror_weak")));
+# elif defined(HAVE_SYS_WEAK_ALIAS_PRAGMA)
+#  pragma weak sudo_warn_strerror_v1 = sudo_warn_strerror_weak
+# elif defined(HAVE_SYS_WEAK_ALIAS_HPSECONDARY)
+#  pragma _HP_SECONDARY_DEF sudo_warn_strerror_weak sudo_warn_strerror_v1
+# elif defined(HAVE_SYS_WEAK_ALIAS_CRIDUPLICATE)
+#  pragma _CRI duplicate sudo_warn_strerror_v1 as sudo_warn_strerror_weak
+# endif
+
+#endif /* HAVE_SYS_WEAK_ALIAS */