ART vectorizer.

Rationale:
Make SIMD great again with a retargetable and easily extendable vectorizer.

Provides a full x86/x86_64 and a proof-of-concept ARM implementation. Sample
improvement (without any perf tuning yet) for Linpack on x86 is about 20% to 50%.

Test: test-art-host, test-art-target (angler)
Bug: 34083438, 30933338

Change-Id: Ifb77a0f25f690a87cd65bf3d5e9f6be7ea71d6c1