FWIW it turns out that IFUNC resolution is supported by gcc for riscv
targets where all the underlying tools support them (which, in current
riscv-gnu-toolchain, they do). Support is detected and enabled here:
https://github.com/gcc-mirror/gcc/blob/master/gcc/configure.ac#L3027

Having a stable finalised kernel/user interface for caps would help, but
for this purpose a few CSR reads should hopefully be enough to make sane
decisions.