Kernel/LibC: Implement fchdir, cleanup chdir and getcwd

userspace/libraries/LibC/include/sys/syscall.h

@@ -32,8 +32,9 @@ __BEGIN_DECLS
 	O(SYS_GET_GID,			getgid)			\
 	O(SYS_GET_EUID,			geteuid)		\
 	O(SYS_GET_EGID,			getegid)		\
-	O(SYS_GET_PWD,			getpwd)			\
-	O(SYS_SET_PWD,			setpwd)			\
+	O(SYS_GETCWD,			getcwd)			\
+	O(SYS_CHDIR,			chdir)			\
+	O(SYS_FCHDIR,			fchdir)			\
 	O(SYS_CLOCK_GETTIME,	clock_gettime)	\
 	O(SYS_PIPE,				pipe)			\
 	O(SYS_DUP2,				dup2)			\

userspace/libraries/LibC/unistd.cpp

@@ -426,7 +426,7 @@ char* getcwd(char* buf, size_t size)
 		return nullptr;
 	}
 
-	if (syscall(SYS_GET_PWD, buf, size) == 0)
+	if (syscall(SYS_GETCWD, buf, size) == 0)
 		return nullptr;
 
 	return buf;
@@ -434,7 +434,12 @@ char* getcwd(char* buf, size_t size)
 
 int chdir(const char* path)
 {
-	return syscall(SYS_SET_PWD, path);
+	return syscall(SYS_CHDIR, path);
+}
+
+int fchdir(int fildes)
+{
+	return syscall(SYS_FCHDIR, fildes);
 }
 
 int chown(const char* path, uid_t owner, gid_t group)