Allow MySensor specific boards to be compiled with warnings enabled

This commit enables the Arduino IDE to configure MySensor specific
boards with more verbose warnings just as official Arduino boards.

hardware/MySensors/avr/platform.txt

@@ -11,17 +11,23 @@ version=1.6.0
 # AVR compile variables
 # --------------------- 
 
+compiler.warning_flags=-w
+compiler.warning_flags.none=-w
+compiler.warning_flags.default=
+compiler.warning_flags.more=-Wall
+compiler.warning_flags.all=-Wall -Wextra
+
 # Default "compiler.path" is correct, change only if you want to overidde the initial value
 compiler.path={runtime.tools.avr-gcc.path}/bin/
 compiler.c.cmd=avr-gcc
-compiler.c.flags=-c -g -Os -w -ffunction-sections -fdata-sections -MMD
+compiler.c.flags=-c -g -Os {compiler.warning_flags} -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 -Os -Wl,--gc-sections
+compiler.c.elf.flags={compiler.warning_flags} -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 -fno-threadsafe-statics -MMD
+compiler.cpp.flags=-c -g -Os {compiler.warning_flags} -fno-exceptions -ffunction-sections -fdata-sections -fno-threadsafe-statics -MMD
 compiler.ar.cmd=avr-ar
 compiler.ar.flags=rcs
 compiler.objcopy.cmd=avr-objcopy