errno: add ENOTEMPTY for rmdir()

include/errno.h

@@ -25,6 +25,7 @@ extern int errno;
 #define ESPIPE       14   /* File descriptor is unable to seek. */
 #define EISDIR       15   /* File descriptor is a directory. */
 #define ENOTDIR      16   /* File descriptor is not a directory. */
+#define ENOTEMPTY    17   /* Directory is not empty. */
 
 #ifdef __cplusplus
 }

src/libc/string/strerror.c

@@ -19,6 +19,7 @@ static char *errno_strings [] = {
 	[ESPIPE]      = "Illegal seek",
 	[EISDIR]      = "Is a directory",
 	[ENOTDIR]     = "Not a directory",
+	[ENOTEMPTY]   = "Directory not empty",
 };
 
 char *strerror(int e)