Add missing dirent macros (fixes #129)

include/bits/dirent.h

 #ifndef _BITS_DIRENT_H
 #define _BITS_DIRENT_H
 
-#define _DIRENT_SIZE (sizeof dirent)
+// Shamelessly stolen from musl
+#define DT_UNKNOWN 0
+#define DT_FIFO 1
+#define DT_CHR 2
+#define DT_DIR 4
+#define DT_BLK 6
+#define DT_REG 8
+#define DT_LNK 10
+#define DT_SOCK 12
+#define DT_WHT 14
+#define IFTODT(x) ((x)>>12 & 017)
+#define DTTOIF(x) ((x)<<12)
 
 #endif /* _BITS_DIRENT_H */