patch 8.0.1826: configure uses old compiler flag

Problem:    Configure uses old compiler flag.
Solution:   Remove _DARWIN_C_SOURCE. (Kazunobu Kuriyama)
diff --git a/src/version.c b/src/version.c
index 9743283..0348dc1 100644
--- a/src/version.c
+++ b/src/version.c
@@ -762,6 +762,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1826,
+/**/
     1825,
 /**/
     1824,