fix building by Cygwin: Cygwin defines _sys_nerr instead of sys_nerr,
the issue has been introduced in r3788
diff --git a/auto/unix b/auto/unix
index 0160661..5818180 100755
--- a/auto/unix
+++ b/auto/unix
@@ -119,6 +119,18 @@
. auto/feature
+# Cygiwn defines _sys_nerr
+ngx_feature="_sys_nerr"
+ngx_feature_name="NGX_SYS_NERR"
+ngx_feature_run=value
+ngx_feature_incs='#include <errno.h>
+ #include <stdio.h>'
+ngx_feature_path=
+ngx_feature_libs=
+ngx_feature_test='printf("%d", _sys_nerr);'
+. auto/feature
+
+
ngx_feature="localtime_r()"
ngx_feature_name="NGX_HAVE_LOCALTIME_R"
ngx_feature_run=no
