Re-add EOF to bits header

cbindgen can't handle negative numbers, see https://github.com/eqrion/cbindgen/issues/205

include/bits/stdio.h

@@ -1,6 +1,8 @@
 #ifndef _BITS_STDIO_H
 #define _BITS_STDIO_H
 
+#define EOF (-1)
+
 typedef struct FILE FILE;
 
 int fprintf(FILE * stream, const char * fmt, ...);