AGCM4 debug option (#14838)

platformio.ini

 platform      = atmelsam
 board         = adafruit_grandcentral_m4
 framework     = arduino
-build_flags   = ${common.build_flags}
-  -Wl,-Map,$BUILD_DIR/firmware.map -Wl,--cref
+build_flags   = ${common.build_flags} -std=gnu++17
+build_unflags = -std=gnu++11
 lib_deps      = ${common.lib_deps}
 lib_ignore    = U8glib-HAL, TMC26XStepper
 src_filter    = ${common.default_src_filter} +<src/HAL/HAL_SAMD51>
+debug_tool    = jlink