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/qemu.h b/linux-user/qemu.h
index e04a31c..83ad443 100644
--- a/linux-user/qemu.h
+++ b/linux-user/qemu.h
@@ -140,7 +140,7 @@
  * and envelope for the new program. 32 should suffice, this gives
  * a maximum env+arg of 128kB w/4KB pages!
  */
-#define MAX_ARG_PAGES 32
+#define MAX_ARG_PAGES 33
 
 /*
  * This structure is used to hold the arguments that are