build gcc with lto support

The included gcc wasn't built with the linker plugin, so enabling link-time optimization (-flto) fails.
dlopen:'.../arduino-1.6.1/hardware/tools/esp8266/xtensa-lx106-elf/bin/../libexec/gcc/xtensa-lx106-elf/4.8.2/liblto_plugin-0.dll': The specified module could not be found.
Lto not only reduces code size, it can significantly improve performance by doing constant folding for function calls like digitalWrite.
http://nerdralph.blogspot.ca/2014/04/gcc-link-time-optimization-can-fix-bad.html
##

Want to back this issue? **[Post a bounty on it!](https://www.bountysource.com/issues/10284804-build-gcc-with-lto-support?utm_campaign=plugin&utm_content=tracker%2F14245935&utm_medium=issues&utm_source=github)** We accept bounties via [Bountysource](https://www.bountysource.com/?utm_campaign=plugin&utm_content=tracker%2F14245935&utm_medium=issues&utm_source=github).

Inizia dal percorso GCC xtensa-lx106-elf segnalato e dall’errore di caricamento di liblto_plugin-0.dll, quindi traccia come viene compilata e pacchettizzata la toolchain inclusa. Il lavoro è completo quando il GCC incluso contiene un linker plugin funzionante e l’abilitazione di -flto non fallisce più; verificalo con una build ESP8266 che utilizzi LTO.

Scritto dal modello di indicizzazione a partire dal testo della issue.