The test assumed that the 'avx2' target_feature would never be set
and used this fact to verify that unsafe_target_feature would
correctly not even compile test functions maked with that
target_feature. As of CentOS 10 and derivatives, th avx2
target_feature is now set by the system rustc, so let's use a
target_feature less likely to appear in the real world.
Closes#755
* Vendor import unsafe_target_features as curve25519-dalek-derive
Co-authored-by: Jan Bujak <jan@parity.io>
* Remove feature gates from avx2/ifma
* Add buildtime compile diagnostics about backend selection
* Add build script tests
* Documentation changes
* Disable simd related features unless simd was determined via build
* Add note and test about the override warning when unsuccesful
* Reduce complexity in build gating via compile_error
---------
Co-authored-by: Jan Bujak <jan@parity.io>
Co-authored-by: Michael Rosenberg <michael@mrosenberg.pub>
