libpayload: Improve compatibility

Define INT_MAX, EOF and make sure size_t is available.

Change-Id: I1b4b717d2545ea8312ec52339300307a5bd68f8a
Signed-off-by: Patrick Georgi <patrick.georgi@secunet.com>
Reviewed-on: http://review.coreboot.org/104
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
diff --git a/payloads/libpayload/include/stdarg.h b/payloads/libpayload/include/stdarg.h
index 7a6244e..077645f 100644
--- a/payloads/libpayload/include/stdarg.h
+++ b/payloads/libpayload/include/stdarg.h
@@ -30,6 +30,7 @@
 #ifndef _LIBPAYLOAD_STDARG_H
 #define _LIBPAYLOAD_STDARG_H
 
+#include <stddef.h>
 #include_next <stdarg.h>
 
 /**