Define ssize_t if necessary.

Change-Id: I63801cc1f09be5e4ca20a6da7ec3366ba6441afd
diff --git a/libc/include/stdio.h b/libc/include/stdio.h
index d0121c6..ca78092 100644
--- a/libc/include/stdio.h
+++ b/libc/include/stdio.h
@@ -60,6 +60,11 @@
 typedef	unsigned long    size_t;
 #endif
 
+#ifndef _SSIZE_T_DEFINED_
+#define _SSIZE_T_DEFINED_
+typedef long int  ssize_t;
+#endif
+
 #ifndef	_OFF_T_DEFINED_
 #define	_OFF_T_DEFINED_
 typedef	long    off_t;