To run 32bit rustc you need enabled cp15 barrier emulation. (This is removed in ARMV8 arch and needed to emulated by the kernel)
Please reenable like in legacy kernel 4.9:
CONFIG_ARMV8_DEPRECATED=y
CONFIG_SWP_EMULATION=y
CONFIG_CP15_BARRIER_EMULATION=y
CONFIG_SETEND_EMULATION=y