--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gcc/config/avr/avrlibc.h	Fri Oct 27 22:46:09 2017 +0900
@@ -0,0 +1,40 @@
+/* Definitions of target machine for the GNU compiler collection
+   for Atmel AVR micro controller if configured for AVR-Libc.
+   Copyright (C) 2012-2017 Free Software Foundation, Inc.
+   Contributed by Georg-Johann Lay (avr@gjlay.de)
+
+This file is part of GCC.
+
+GCC is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 3, or (at your option)
+any later version.
+
+GCC is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with GCC; see the file COPYING3.  If not see
+<http://www.gnu.org/licenses/>.  */
+
+#undef  LIB_SPEC
+#define LIB_SPEC                                \
+  "%{!mmcu=avr1:-lc} %(avrlibc_devicelib)"
+
+// AVR-Libc implements functions from libgcc.a in libm.a, see PR54461.
+// For a list of functions which are provided by libm.a and are
+// omitted from libgcc.a see libgcc's t-avrlibc.
+
+#undef  LIBGCC_SPEC
+#define LIBGCC_SPEC                             \
+  "%{!mmcu=avr1:-lgcc -lm}"
+
+#undef  STARTFILE_SPEC
+#define STARTFILE_SPEC                          \
+  " %(avrlibc_startfile) "
+
+#undef  LINK_GCC_C_SEQUENCE_SPEC
+#define LINK_GCC_C_SEQUENCE_SPEC \
+  "--start-group %G %L --end-group"