This is needed to unblock nightly toolchains, which are currently failing to build with an assertion:
```
swift-frontend: /home/build-user/build/buildbot_linux/llvm-linux-x86_64/tools/clang/include/clang/AST/TypeNodes.inc:79: TypeInfo clang::ASTContext::getTypeInfoImpl(const Type *) const: Assertion `!T->isDependentType() && "should not see dependent types here"' failed.
```
rdar://150067288
The C++ interop benchmarks were only running when building with CMake, not with SwiftPM, because of a bug that was only triggering with SwiftPM. That bug seems to be fixed now.
This adds an `import CxxStdlib` statement which fixes compilation. It should be redundant, but it works around a bug that got exposed by an change in explicit modules (rdar://128520766).
This will bring back the performance numbers while the underlying issue is being investigated.
`std::vector::const_iterator` is now automatically conformed to `UnsafeCxxRandomAccessIterator`, and `std::vector` is conformed to `CxxRandomAccessCollection`.
The manually added conformances are now redundant.
