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Description
Problem
When testing with miri one often has to enable target features (all SIMD features) to be sure to test SIMD instructions which tend to contain unsafe code. This requires target_feature to be set in both RUSTFLAGS and RUSTDOCFLAGS. Not only is this annoying but also a footgun. From my understanding miri just passes the arguments along so it's a cargo issue.
Proposed Solution
Consider adding an argument that can set the target features as needed. Even better, also have an argument that enables all SIMD features.
Alternatively it could be decided that this is too niche and should be handled by miri and that may be the only tool that currently needs it, in which case I'll be happy to open an issue there.
Notes
I've opened this as requested in #12739 (comment)