Ignore return value from strerror_r.

It seems like newer glibc added warn_unused_result to this function.
Try harder to ignore the result.

generator/lua.ml

@@ -67,6 +67,8 @@ let generate_lua_c () =
 #endif
 #endif
 
+#include \"ignore-value.h\"
+
 #include <guestfs.h>
 #include \"guestfs-utils.h\"
 
@@ -163,7 +165,7 @@ guestfs_int_lua_create (lua_State *L)
 
   g = guestfs_create_flags (flags);
   if (!g) {
-    strerror_r (errno, err, sizeof err);
+    ignore_value (strerror_r (errno, err, sizeof err));
     return luaL_error (L, \"Guestfs.create: cannot create handle: %%s\", err);
   }
 
@@ -242,7 +244,7 @@ error__tostring (lua_State *L)
   msg = luaL_checkstring (L, -1);
 
   if (code) {
-    strerror_r (code, err, sizeof err);
+    ignore_value (strerror_r (code, err, sizeof err));
     lua_pushfstring (L, \"%%s: %%s\", msg, err);
   }
   else
@@ -653,7 +655,7 @@ get_string_list (lua_State *L, int index)
 
   strs = malloc ((len+1) * sizeof (char *));
   if (strs == NULL) {
-    strerror_r (errno, err, sizeof err);
+    ignore_value (strerror_r (errno, err, sizeof err));
     luaL_error (L, \"get_string_list: malloc failed: %%s\", err);
     /*NOTREACHED*/
     return NULL;

lib/errors.c

@@ -47,6 +47,7 @@
 #include <libintl.h>
 
 #include "c-ctype.h"
+#include "ignore-value.h"
 
 #include "guestfs.h"
 #include "guestfs-internal.h"
@@ -329,7 +330,7 @@ guestfs_int_perrorf (guestfs_h *g, const char *fs, ...)
 
   if (err < 0) return;
 
-  strerror_r (errnum, buf, sizeof buf);
+  ignore_value (strerror_r (errnum, buf, sizeof buf));
 
   msg = safe_realloc (g, msg, strlen (msg) + 2 + strlen (buf) + 1);
   strcat (msg, ": ");