* fix build after stabilization of cfg_target_feature and target_feature
* fix doc tests
* fix spurious unused_attributes warning
* fix more unused attribute warnings
* More unnecessary target features
* Remove no longer needed trait imports
* Remove fixed upstream workarounds
* Fix parsing the #[assert_instr] macro
Following upstream proc_macro changes
* Fix form and parsing of #[simd_test]
* Don't use Cargo features for testing modes
Instead use RUSTFLAGS with `--cfg`. This'll help us be compatible with the
latest Cargo where a tweak to workspaces and features made the previous
invocations we had invalid.
* Don't thread RUSTFLAGS through docker
* Re-gate on x86 verification
Closes#411
