arch: arm: swap_helper.S: safe guarding GTEXT(z_arm_do_syscall)
arch: arm: swap_helper.S: safe guarding GTEXT(z_arm_do_syscall)

z_arm_do_syscall is only defined and used when CONFIG_USERSPACE=y.

Defining the symbol z_arm_do_syscall in assembly without a corresponding
implementation is fine for GNU ld as long as the function is not
actively called, but armlink fails to link in such cases.

Safegaurd GTEXT(z_arm_do_syscall) so the symbol is only referenced when
actively used, that is when CONFIG_USERSPACE=y.

Signed-off-by: Torsten Rasmussen <a7c5b1d5a1f41fce6edfa3f7c2392ae0c59deafe@nordicsemi.no>

zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,galak/zephyr,galak/zephyr,galak/zephyr,finikorg/zephyr,finikorg/zephyr,galak/zephyr,finikorg/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr