Enable C++11 support

This uses the gnu++11 standard, which is C++11 with GNU extensions.
C++11 should be full compatible with the previously used C++98
standards, so all pre-existing sketches should continue to work.

Author: matthijskooijman

hardware/arduino/avr/platform.txt

@@ -21,7 +21,7 @@ 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 -std=gnu++98 -fno-exceptions -ffunction-sections -fdata-sections -MMD
+compiler.cpp.flags=-c -g -Os -w -std=gnu++11 -fno-exceptions -ffunction-sections -fdata-sections -MMD
 compiler.ar.cmd=avr-ar
 compiler.ar.flags=rcs
 compiler.objcopy.cmd=avr-objcopy