Fix humongous bug with fdopendir on mac

https://opensource.apple.com/source/Libc/Libc-1244.1.7/include/dirent.h.auto.html

ccall picks the wrong one, causes crashes and truncated d_name
entries. Wrapping the function in a small C shim, as well as
using the CAPI, fixes this.

hpath-posix/cbits/dirutils.c

@@ -1,7 +1,7 @@
 #include "dirutils.h"
+
 unsigned int
     __posixdir_d_type(struct dirent* d)
     {
       return(d -> d_type);
     }
-

hpath-posix/cbits/dirutils.h

@@ -7,7 +7,9 @@
 #include <sys/stat.h>
 #include <fcntl.h>
 
+
 extern unsigned int
     __posixdir_d_type(struct dirent* d)
     ;
+
 #endif