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>

payloads/libpayload/include/stdio.h

@@ -32,6 +32,8 @@
 
 #include <stddef.h>
 
+#define EOF (-1)
+
 typedef struct _FILE FILE;
 
 extern FILE *stdout, *stdin, *stderr;