gcc: Adding -w flag to compiler.c.elf.flags in order to avoid printin…

…g ISR warning http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59396

hardware/arduino/avr/platform.txt

@@ -15,7 +15,9 @@ version=1.5.6
 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.elf.flags=-Os -Wl,--gc-sections -flto
+# -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=-Os -Wl,--gc-sections -w -flto
 compiler.c.elf.cmd=avr-gcc
 compiler.S.flags=-c -g -x assembler-with-cpp
 compiler.cpp.cmd=avr-g++