https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67373
--- Comment #5 from Senthil Kumar Selvaraj <senthil_kumar.selvaraj at atmel dot com> --- The last released version of avr-libc (1.8.1) doesn't properly work with the spec file based device support approach introduced in 5.x. As the GCC 5 release notes (https://gcc.gnu.org/gcc-5/changes.html) describes The AVR port uses a new scheme to describe supported devices: For each supported device the compiler provides a device-specific spec file. If the compiler is used together with AVR-LibC, this requires at least GCC 5.2 and a version of AVR-LibC which implements feature #44574. Can you try building with the trunk version of avr-libc? That should work fine.
