Add fopendir() to fs_darwin.cpp and fix symlinkat().

This completes 2/3 of #8857 and is courtesy of nielx.

headers/build/host/darwin/dirent.h

@@ -0,0 +1,16 @@
+#ifndef _HAIKU_BUILD_COMPATIBILITY_DARWIN_DIRENT
+#define _HAIKU_BUILD_COMPATIBILITY_DARWIN_DIRENT
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#include_next <dirent.h>
+
+DIR* fdopendir(int fd);	
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif	// _HAIKU_BUILD_COMPATIBILITY_DARWIN_DIRENT

headers/build/host/darwin/endian.h

@@ -6,6 +6,6 @@
 #define	__LITTLE_ENDIAN	LITTLE_ENDIAN
 #define	__BIG_ENDIAN	BIG_ENDIAN
 #define	__PDP_ENDIAN	PDP_ENDIAN
-#define __BYTE_ORDER    BYTE_ORDER
+#define	__BYTE_ORDER	BYTE_ORDER
 
 #endif	// _HAIKU_BUILD_COMPATIBILITY_DARWIN_ENDIAN

headers/build/host/darwin/sys/stat.h

@@ -14,7 +14,7 @@
 	__BEGIN_DECLS
 
 	/* assume that futimens() and utimensat() aren't available */
-	int	futimens(int fd, const struct timespec times[2]);
+	int futimens(int fd, const struct timespec times[2]);
 	int utimensat(int fd, const char* path, const struct timespec times[2],
 		int flag);