Fix ARM 32 bits build, prfm is a 64 bits instruction.

[devnexen]

No description provided.

[mjp41]

Do you know why the ARM 32-bit CI was not failing? What should we change on that pipeline?

[devnexen]

I do not really know azure pipelines, I do not know if the 32 bits build are genuine 32 bits or labels ?
Anyway I was just testing the build on a raspberry.

[davidchisnall]

@devnexen, what's the compiler that you're using? I think we'll probably use __builtin_prefetch() with clang and only use this version on gcc Arm. We might want to expand the CI to try gcc on the Arm builds.

[devnexen]

ah right I did not notice but I was using gcc indeed :)

[mjp41]

@devnexen, thanks for fixing this.