Yes, it looks like we'd need to conditionally compile these functions
in ARM mode and use the v6 barrier instead of dmb ("mcr p15, #0, r0,
c7, c10, #5" I believe) to support the ARM1176JZF-S in RPi. You'd
probably also want the build system to use an explicit -march=armv6 or
something so you're not at the mercy of how the host compiler was
configured.
I suspect you're the first person to try and get compiler-rt going for
pre-v7 hardware, which most of us prefer to pretend never happened
most of the time.