This commit adds a new `libcxx` feature that enables testing libc++'s
implementation of `std::regex` when combined with the `re-stdcpp`
feature.
See also: https://libcxx.llvm.org/docs/UsingLibcxx.html
The regex_macros crate hasn't been maintained in quite some time, and has
been broken. Nobody has complained. Given the fact that there are no
immediate plans to improve the situation, and the fact that it is slower
than the runtime engine, we simply remove it.
This makes a few touch ups to benchmarks:
1. Add some regex-dna related benchmarks.
2. Change use of RUSTFLAGS="-C target-feature=+ssse3" to
RUSTFLAGS="-C target-cpu=native".
3. Switch order of parameters to regex-run-one benchmarking tool.
This uses the "Teddy" algorithm, as learned from the Hyperscan regular
expression library: https://01.org/hyperscan
This support optional, subject to the following:
1. A nightly compiler.
2. Enabling the `simd-accel` feature.
3. Adding `RUSTFLAGS="-C target-feature=+ssse3"` when compiling.