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);
 

src/build/libroot/fs_darwin.cpp

@@ -213,6 +213,30 @@ fchownat(int fd, const char* path, uid_t owner, gid_t group, int flag)
 }
 
 
+DIR*
+fdopendir(int fd)
+{
+	struct stat st;
+	if (fstat(fd, &st)) {
+		// failed to get the stat info for fd, fstat() sets errno
+		return NULL;
+	}
+
+	if (!S_ISDIR(st.st_mode)) {
+		errno = ENOTDIR;
+		return NULL;
+	}
+
+	char path[MAXPATHLEN];
+	if (fcntl(fd, F_GETPATH, path) < 0) {
+		// failed to get the path of fd, fcntl() sets errno
+		return NULL;
+	}
+
+	return opendir(path);
+}
+
+
 int
 fstatat(int fd, const char *path, struct stat *st, int flag)
 {
@@ -391,11 +415,12 @@ symlinkat(const char *oldPath, int fd, const char *newPath)
 		return -1;
 	}
 
-	char oldFullPath[MAXPATHLEN];
+	// newPath is relative to the fd
-	if (get_path(fd, oldPath, oldFullPath) < 0)
+	char newFullPath[MAXPATHLEN];
+	if (get_path(fd, newPath, newFullPath) < 0)
 		return -1;
 
-	return symlink(oldFullPath, newPath);
+	return symlink(oldPath, newFullPath);
 }