toolchain: gcc: Remove ref. to undefined sym. CONFIG_ISA_ARM
toolchain: gcc: Remove ref. to undefined sym. CONFIG_ISA_ARM

This Kconfig symbol was removed in commit cb04620fbd ("remove make/
directory").

Signed-off-by: Ulf Magnusson <01743f1c1deb1fe75271d62edb65757d98ac0bcb@nordicsemi.no>

zephyrproject-rtos/zephyr,ldts/zephyr,nashif/zephyr,GiulianoFranchetto/zephyr,ldts/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,nashif/zephyr,finikorg/zephyr,finikorg/zephyr,finikorg/zephyr,nashif/zephyr,GiulianoFranchetto/zephyr,galak/zephyr,GiulianoFranchetto/zephyr,ldts/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,galak/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,galak/zephyr,ldts/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,Vudentz/zephyr,Vudentz/zephyr,GiulianoFranchetto/zephyr,Vudentz/zephyr,ldts/zephyr,GiulianoFranchetto/zephyr,finikorg/zephyr,finikorg/zephyr,Vudentz/zephyr