linux-user: increment MAX_ARG_PAGES

There's a error When doing something like that :
find / -type f -print0 | xargs -0 echo

[ done in a arm chroot with qemu-arm and linux binfmt stuff or with
find / -type f -print0 | qemu-arm -L <path> <path>/usr/bin/xargs -0
echo ]

Doing this outsite qemu is fine. The problem was the huge number of
parameters. Increasing MAX_ARG_PAGES is fixing that.

While I was at it, I've modified linux-user/main.c to report error code
of loader_exec. It helps to debug/know what's wrong.

Signed-off-by: Arnaud Patard <arnaud.patard@rtp-net.org>
Signed-off-by: Riku Voipio <riku.voipio@iki.fi>
diff --git a/linux-user/main.c b/linux-user/main.c
index 7eabd0c..345d338 100644
--- a/linux-user/main.c
+++ b/linux-user/main.c
@@ -2372,6 +2372,7 @@
     envlist_t *envlist = NULL;
     const char *argv0 = NULL;
     int i;
+    int ret;
 
     if (argc <= 1)
         usage();
@@ -2576,9 +2577,10 @@
     env->opaque = ts;
     task_settid(ts);
 
-    if (loader_exec(filename, target_argv, target_environ, regs,
-        info, &bprm) != 0) {
-        printf("Error loading %s\n", filename);
+    ret = loader_exec(filename, target_argv, target_environ, regs,
+        info, &bprm);
+    if (ret != 0) {
+        printf("Error %d while loading %s\n", ret, filename);
         _exit(1);
     }