See https://bugs.gentoo.org/649168

Patch by: Matt Whitlock <gentoo@mattwhitlock.name>

diff -Naur a/tools/fibmap.c b/tools/fibmap.c
--- a/tools/fibmap.c	2018-03-01 00:09:24.861919778 +0000
+++ b/tools/fibmap.c	2018-03-01 17:31:48.854604556 +0000
@@ -15,6 +15,7 @@
 #ifndef O_LARGEFILE
 #define O_LARGEFILE 0
 #endif
+#include "config.h"
 #include <unistd.h>
 #include <string.h>
 #include <stdlib.h>