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

platform.txt

@@ -25,7 +25,7 @@ compiler.c.elf.flags=-Os -Wl,--gc-sections
 compiler.S.cmd=arm-none-eabi-gcc
 compiler.S.flags=-c -g -x assembler-with-cpp -mthumb
 compiler.cpp.cmd=arm-none-eabi-g++
-compiler.cpp.flags=-c -g -Os {compiler.warning_flags} -std=gnu++98 -ffunction-sections -fdata-sections -nostdlib -fno-threadsafe-statics --param max-inline-insns-single=500 -fno-rtti -fno-exceptions -Dprintf=iprintf -MMD
+compiler.cpp.flags=-c -g -Os {compiler.warning_flags} -std=gnu++11 -ffunction-sections -fdata-sections -nostdlib -fno-threadsafe-statics --param max-inline-insns-single=500 -fno-rtti -fno-exceptions -Dprintf=iprintf -MMD
 compiler.ar.cmd=arm-none-eabi-ar
 compiler.ar.flags=rcs
 compiler.objcopy.cmd=arm-none-eabi-objcopy