remap_neon: use register r12 instead of r7

Merged Tanu Kaskinen requested to merge tanuk/pulseaudio:fix-thumb-frame-pointer into master

When the Thumb instructions set is used and frame pointers are enabled (-fno-omit-frame-pointer), r7 can't be used, because it's used for the frame pointer. Trying to use r7 caused the compilation to fail.

Thanks to Andre McCurdy for suggesting[1] this fix, all I had to do was to test that it works. The code builds now, and cpu-remap-test also succeeds.


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