platform: force c++17

Author: facchinm

Diff for: platform.txt

@@ -19,11 +19,11 @@ compiler.path={build.compiler_path}
 compiler.c.cmd={build.crossprefix}gcc
 compiler.c.flags=-g -c {compiler.warning_flags} {compiler.zephyr.defines} {compiler.zephyr.cflags} {compiler.zephyr.arch.define} -MMD -mcpu={build.mcu} {build.float-abi} {build.fpu}
 compiler.c.elf.cmd={build.crossprefix}g++
-compiler.c.elf.flags=-r -Wl,--gc-sections -e main
+compiler.c.elf.flags=-r -Wl,--gc-sections -e main -mcpu={build.mcu} {build.float-abi} {build.fpu} -std=c++17
 compiler.S.cmd={build.crossprefix}g++
 compiler.S.flags=-c -x assembler-with-cpp -mcpu={build.mcu} {build.fpu}
 compiler.cpp.cmd={build.crossprefix}g++
-compiler.cpp.flags=-g -Os -c {compiler.warning_flags} {compiler.zephyr.defines} {compiler.zephyr.cxxflags} {compiler.zephyr.arch.define} -MMD -mcpu={build.mcu} {build.float-abi} {build.fpu}
+compiler.cpp.flags=-g -Os -std=c++17 -c {compiler.warning_flags} {compiler.zephyr.defines} {compiler.zephyr.cxxflags} {compiler.zephyr.arch.define} -MMD -mcpu={build.mcu} {build.float-abi} {build.fpu}
 compiler.ar.cmd={build.crossprefix}ar
 compiler.ar.flags=rcs
 compiler.objcopy.cmd=