Reverting -flto flag from AVR core until all compatibility problems are worked out.

For more info:
https://groups.google.com/a/arduino.cc/d/msg/developers/21G5w2HbUOg/NRMW6c9OIFUJ

Author: cmaglie

hardware/arduino/avr/platform.txt

@@ -14,14 +14,14 @@ 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 -flto
+compiler.c.flags=-c -g -Os -w -ffunction-sections -fdata-sections -MMD
 # -w flag added to avoid printing a wrong warning http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59396
 # This is fixed in gcc 4.8.3 and will be removed as soon as we update the toolchain
-compiler.c.elf.flags=-w -flto -Os -Wl,--gc-sections
+compiler.c.elf.flags=-w -Os -Wl,--gc-sections
 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 -flto
+compiler.cpp.flags=-c -g -Os -w -fno-exceptions -ffunction-sections -fdata-sections -MMD
 compiler.ar.cmd=avr-ar
 compiler.ar.flags=rcs
 compiler.objcopy.cmd=avr-objcopy