Fixed building --with-debug, broken by 6fce16b1fc10.

src/os/unix/ngx_files.c

diff --git a/src/os/unix/ngx_files.c b/src/os/unix/ngx_files.c
index 60b737f..417b598 100644
--- a/src/os/unix/ngx_files.c
+++ b/src/os/unix/ngx_files.c
@@ -344,7 +344,7 @@
             err = ngx_errno;
 
             if (err == NGX_EINTR) {
-                ngx_log_debug0(NGX_LOG_DEBUG_EVENT, c->log, err,
+                ngx_log_debug0(NGX_LOG_DEBUG_CORE, file->log, err,
                                "writev() was interrupted");
                 goto eintr;
             }