Add basic errno support.

Needed for hash table support; probably useful in a lot of other
places as well.

Signed-off-by: Wolfgang Denk <wd@denx.de>
diff --git a/lib/errno.c b/lib/errno.c
new file mode 100644
index 0000000..8330a8f
--- /dev/null
+++ b/lib/errno.c
@@ -0,0 +1 @@
+int errno = 0;