User registers fsr,, fcr, f64r_lo, f64_hi, f64s not implemented (LLVM-71)

[arjanmels]

The RUR and WUR instructions are not implemented for user registers: fsr,, fcr, f64r_lo, f64_hi, f64s.

[andreisfr]

@arjanmels, please try to use latest branch xtensa_release_9.0.1, it impements fsr..f64s registers.

[arjanmels]

@andreisfr Thanks and apologies. I was using https://github.com/MabezDev/rust-xtensa, turns out that the llvm submodule indeed points to an old commit, not the latest.