Update copyright years.

From-SVN: r256169
diff --git a/libgcc/dfp-bit.c b/libgcc/dfp-bit.c
index 8718d94..fbd75d7 100644
--- a/libgcc/dfp-bit.c
+++ b/libgcc/dfp-bit.c
@@ -1,5 +1,5 @@
 /* This is a software decimal floating point library.
-   Copyright (C) 2005-2017 Free Software Foundation, Inc.
+   Copyright (C) 2005-2018 Free Software Foundation, Inc.
 
 This file is part of GCC.