Add vst1_* neon intrinsics.

[hasenbanck]

I took the vld1_* implementation as an example while writing the vst1_* implementation.

While the arm intrinsics use the LLVM provided intrinsics, I had to copy the approach taken by the SSE unaligned store intrinsics for the aarch64 implementation.

I also ported the SSE tests for the unaligned stores.

I'm not really sure about the #[cfg_attr(test, assert_instr(*))] asserts, since I couldn't find a away how to verify these tests. It would be great if somebody could hint me how to tests these.

[rust-highfive]

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