Move errno.h functions into their own directory.

libc/Makefile

@@ -25,7 +25,7 @@ ctype/ctype.o \
 dirent/alphasort.o \
 dirent/dir.o \
 dirent/versionsort.o \
-errno.o \
+errno/errno.o \
 fabs.o \
 fbufsize.o \
 fclose.o \

libc/errno/errno.cpp

@@ -17,7 +17,7 @@
     You should have received a copy of the GNU Lesser General Public License
     along with the Sortix C Library. If not, see <http://www.gnu.org/licenses/>.
 
-    errno.cpp
+    errno/errno.cpp
     Value storing a numeric value representing the last occured error.
 
 *******************************************************************************/