Fix opt_imax() call

Not all architectures have a time_t defined the same way.  To make
sure we get the same result, we need to cast &checkoffset to (intmax_t *)
and make sure that intmax_t is defined somehow.

To make really sure we don't pass a variable with the wrong size down
to opt_imax(), we use a temporary intmax_t.
Reviewed-by: NRich Salz <rsalz@openssl.org>

apps/apps.h

@@ -145,6 +145,8 @@ int opt_umax(const char *value, uintmax_t *result);
 # else
 #  define opt_imax opt_long
 #  define opt_umax opt_ulong
+#  define intmax_t long
+#  define uintmax_t unsigned long
 # endif
 
 int app_RAND_load_file(const char *file, int dont_warn);

apps/x509.c

@@ -468,12 +468,16 @@ int x509_main(int argc, char **argv)
             break;
         case OPT_CHECKEND:
             checkend = 1;
-            if (!opt_imax(opt_arg(), &checkoffset))
-                goto opthelp;
-            if (checkoffset != (time_t)checkoffset) {
-                BIO_printf(bio_err, "%s: checkend time out of range %s\n",
-                           prog, opt_arg());
-                goto opthelp;
+            {
+                intmax_t temp = 0;
+                if (!opt_imax(opt_arg(), &temp))
+                    goto opthelp;
+                checkoffset = (time_t)temp;
+                if ((intmax_t)checkoffset != temp) {
+                    BIO_printf(bio_err, "%s: checkend time out of range %s\n",
+                               prog, opt_arg());
+                    goto opthelp;
+                }
             }
             break;
         case OPT_CHECKHOST: