Enabling link-time optimization. See arduino#660

Author: Federico Fissore

hardware/arduino/avr/platform.txt

@@ -14,12 +14,12 @@ version=1.5.6
 # Default "compiler.path" is correct, change only if you want to overidde the initial value
 compiler.path={runtime.ide.path}/hardware/tools/avr/bin/
 compiler.c.cmd=avr-gcc
-compiler.c.flags=-c -g -Os -w -ffunction-sections -fdata-sections -MMD
-compiler.c.elf.flags=-Os -Wl,--gc-sections
+compiler.c.flags=-c -g -Os -w -ffunction-sections -fdata-sections -MMD -flto
+compiler.c.elf.flags=-Os -Wl,--gc-sections -flto
 compiler.c.elf.cmd=avr-gcc
 compiler.S.flags=-c -g -x assembler-with-cpp
 compiler.cpp.cmd=avr-g++
-compiler.cpp.flags=-c -g -Os -w -fno-exceptions -ffunction-sections -fdata-sections -MMD
+compiler.cpp.flags=-c -g -Os -w -fno-exceptions -ffunction-sections -fdata-sections -MMD -flto
 compiler.ar.cmd=avr-ar
 compiler.ar.flags=rcs
 compiler.objcopy.cmd=avr-objcopy