ci: remove RUSTFLAGS, enable unstable

This removes our compile time SIMD flags and replaces them with the
`unstable` feature, which will cause CI to use whatever CPU features are
available.

Ideally, we would test each important CPU feature combinations, but I'd
like to avoid doing that in one CI job and instead split them out into
separate CI jobs to keep CI times low. That requires more work.

ci/after_success.sh

@@ -9,7 +9,6 @@ if [ "$TRAVIS_RUST_VERSION" != "nightly" ] || [ "$TRAVIS_PULL_REQUEST" != "false
   exit 0
 fi
 
-export RUSTFLAGS="-C target-feature=+ssse3"
 env
 
 # Install kcov.

ci/run-kcov

@@ -28,7 +28,7 @@ while true; do
   esac
 done
 
-cargo test --no-run --verbose --jobs 4
+cargo test --no-run --verbose --jobs 4 --features unstable
 for t in ${tests[@]}; do
   kcov \
     --verify \

ci/script.sh

@@ -4,12 +4,6 @@
 
 set -ex
 
-if [ "$TRAVIS_RUST_VERSION" = "nightly" ]; then
-  # We set this once so that all invocations share this setting. This should
-  # help with build times by avoiding excessive re-compiles.
-  export RUSTFLAGS="-C target-feature=+ssse3"
-fi
-
 # Builds the regex crate and runs tests.
 cargo build --verbose
 cargo doc --verbose
@@ -25,7 +19,7 @@ fi
 
 # Run tests. If we have nightly, then enable our nightly features.
 if [ "$TRAVIS_RUST_VERSION" = "nightly" ]; then
-  cargo test --verbose --features 'simd-accel pattern'
+  cargo test --verbose --features unstable
 else
   cargo test --verbose
 fi