[benchmark] Compile and run benchmarks on Linux

[mtake]

Exclude Objective-C or Mach specific implementations, or replace them with POSIX based implementations so that we can compile and run benchmarks on Linux.

(This PR supersedes #7810 in favor of not including unrelated merged commits from other people.)

[mtake]

@gottesmm I noticed #7860 has been merged. I would appreciate if you can do the remaining integration work for building the benchmarks on Linux in the smoketest/full test presets.

[gottesmm]

@mtake It is going to take me time to do it. I have other things on my schedule that are more important. Sorry.

Additionally, that change was actually reverted since some people don't include their buildbot config in presets * looks at lldb * = p. So I didn't see it to update it.

[lplarson]

@swift-ci smoke test

[gottesmm]

@lplarson IMO, we should just get this in as an incremental improvement as long as it does not break the linux build or affect the darwin build. I wish that we did have the infrastructure in place so we could get this on in the normal linux build. But my schedule is not being helpful. I don't want to hold this up.

[lplarson]

@swift-ci benchmark

[swift-ci]

Build comment file:

Build failed before running benchmark.

---

[lplarson]

@swift-ci benchmark

[swift-ci]

Build comment file:

Build failed before running benchmark.

---

[lplarson]

@swift-ci benchmark

[swift-ci]

Build comment file:

Build failed before running benchmark.

---

[mtake]

@lplarson Looks like the build error https://ci.swift.org/job/swift-PR-osx-perf/389/consoleFull#-278967002ee1a197b-acac-4b17-83cf-a53b95139a76 is related to the @phausler's commit
dc783c0#diff-60fab3968490aded2585457736a8b091

[lplarson]

@swift-ci smoke test and merge