Add locations for two additional defines.

The two defines that can later be generated in a user's
own boards.local.txt (or platforms.local.txt) are:
  build.logger_flags
  build.sysview_flags

To be used for the following `#define` identifiers:
  -DCFG_LOGGER=0
  -DCFG_SYSVIEW=0

NOTE: These are NOT defined by default.  This is preparation
for enabling alternative debug output locations.

Author: henrygab

platform.txt

@@ -56,8 +56,9 @@ build.debug_flags=-DCFG_DEBUG=0
 rtos.path={build.core.path}/freertos
 nordic.path={build.core.path}/nordic
 
-
-build.flags.nrf= -DSOFTDEVICE_PRESENT -DARDUINO_NRF52_ADAFRUIT -DNRF52_SERIES -DLFS_NAME_MAX=64 -Ofast {build.debug_flags} "-I{build.core.path}/cmsis/include" "-I{nordic.path}" "-I{nordic.path}/nrfx" "-I{nordic.path}/nrfx/hal" "-I{nordic.path}/nrfx/mdk" "-I{nordic.path}/nrfx/soc" "-I{nordic.path}/nrfx/drivers/include" "-I{nordic.path}/nrfx/drivers/src" "-I{nordic.path}/softdevice/{build.sd_name}_nrf52_{build.sd_version}_API/include" "-I{rtos.path}/Source/include" "-I{rtos.path}/config" "-I{rtos.path}/portable/GCC/nrf52" "-I{rtos.path}/portable/CMSIS/nrf52" "-I{build.core.path}/sysview/SEGGER" "-I{build.core.path}/sysview/Config" "-I{build.core.path}/TinyUSB" "-I{build.core.path}/TinyUSB/Adafruit_TinyUSB_ArduinoCore" "-I{build.core.path}/TinyUSB/Adafruit_TinyUSB_ArduinoCore/tinyusb/src"
+# build.logger_flags and build.sysview_flags and intentionally empty,
+# to allow modification via a user's own boards.local.txt or platform.local.txt files.
+build.flags.nrf= -DSOFTDEVICE_PRESENT -DARDUINO_NRF52_ADAFRUIT -DNRF52_SERIES -DLFS_NAME_MAX=64 -Ofast {build.debug_flags} {build.logger_flags} {build.sysview_flags} "-I{build.core.path}/cmsis/include" "-I{nordic.path}" "-I{nordic.path}/nrfx" "-I{nordic.path}/nrfx/hal" "-I{nordic.path}/nrfx/mdk" "-I{nordic.path}/nrfx/soc" "-I{nordic.path}/nrfx/drivers/include" "-I{nordic.path}/nrfx/drivers/src" "-I{nordic.path}/softdevice/{build.sd_name}_nrf52_{build.sd_version}_API/include" "-I{rtos.path}/Source/include" "-I{rtos.path}/config" "-I{rtos.path}/portable/GCC/nrf52" "-I{rtos.path}/portable/CMSIS/nrf52" "-I{build.core.path}/sysview/SEGGER" "-I{build.core.path}/sysview/Config" "-I{build.core.path}/TinyUSB" "-I{build.core.path}/TinyUSB/Adafruit_TinyUSB_ArduinoCore" "-I{build.core.path}/TinyUSB/Adafruit_TinyUSB_ArduinoCore/tinyusb/src"
 
 # usb flags
 build.flags.usb= -DUSBCON -DUSE_TINYUSB -DUSB_VID={build.vid} -DUSB_PID={build.pid} '-DUSB_MANUFACTURER={build.usb_manufacturer}' '-DUSB_PRODUCT={build.usb_product}'