message: Add the ability to specifiy the name of an Xtensa core when building for the
  XPG platform.
diff: # Settings for Xtensa XPG toolchain.
  +# REQUIRED:
  +# - XTENSA_CORE: The name of the core to use, will cause a compiler exception
  +# without providing a core.
  ifeq ($(TARGET), xtensa-xpg)
  TARGET_ARCH := xtensa-xpg
  - # TODO(kreeger): Enable the ability to pass a different core:
  PLATFORM_ARGS = \
  - --xtensa-core=hifi3_bd5 \
  + --xtensa-core=$(XTENSA_CORE) \
  -g -O2 \
  -fmessage-length=0 \
  -clang
  