Add experimental support for customisable benchmarking

[Zentrik]

Replaces #325 (closes #325)

This pr adds the ability to run a custom benchmarking function which has hooks to inject in custom functions. The current design supports running perf on a benchmark (see https://github.com/Zentrik/BenchmarkToolsPlusLinuxPerf.jl) and profiling benchmarks (excluding the setup, teardown and gcscrub which the current bprofile includes).

[DilumAluthge]

I haven't added tests, but given the CI doesn't have perf available, not sure how useful it would be.

We might need to set up Buildkite CI on this repo. @vchuravy @staticfloat

[Zentrik]

I'd like to mark this feature as experimental or something to that effect so that we can make breaking changes to it without making a breaking change to BenchmarkTools.
The changes to samplefunc are largely just so that it matches customisable_func (theoretically it reduces overhead by a couple of instructions but that's not noticeable) and also so the hooks for samplefunc are exposed.

I'll make a separate pr removing Buildkite.

I've moved the LinuxPerf stuff to https://github.com/Zentrik/BenchmarkToolsPlusLinuxPerf.jl.

I do have a version of bprofile that uses this functionality to only profile the relevant stuff, but because samples are generally quite short (on the order of microseconds) not much gets profiled making it pretty useless.

bprofile_setup_prehook(_) = Profile.check_init()
function bprofile_prehook()
    results = samplefunc_prehook()
    status = ccall(:jl_profile_start_timer, Cint, ())
    if status < 0
        error(Profile.error_codes[status])
    end
    return results
end
function bprofile_posthook()
    Profile.stop_timer()
    return samplefunc_posthook()
end

# """
#     @bprofile expression [other parameters...]

# Run `@benchmark` while profiling. This is similar to

#     @profile @benchmark expression [other parameters...]

# but the profiling is applied only to the main
# execution (after compilation and tuning).
# The profile buffer is cleared prior to execution.

# View the profile results with `Profile.print(...)`.
# See the profiling section of the Julia manual for more
# information.
# """
macro bprofile(args...)
    _, params = prunekwargs(args...)
    if !haskw(args, :gctrial)
        args = (args..., Expr(:kw, :gctrial, false))
    end
    if !haskw(args, :gcsample)
        args = (args..., Expr(:kw, :gcsample, false))
    end
    tmp = gensym()
    return esc(
        quote
            local $tmp = $BenchmarkTools.@benchmarkable $(args...)
            $(
                if hasevals(params)
                    :(run(
                        $tmp, $BenchmarkTools.Parameters($tmp.params; evals=1); warmup=false
                    ))
                else
                    :($BenchmarkTools.tune!($tmp))
                end
            )
            $BenchmarkTools.Profile.stop_timer()
            $BenchmarkTools.Profile.clear()
            $BenchmarkTools.run(
                $tmp;
                setup_prehook=$BenchmarkTools.bprofile_setup_prehook,
                prehook=$BenchmarkTools.bprofile_prehook,
                posthook=$BenchmarkTools.bprofile_posthook,
                sample_result=$BenchmarkTools.samplefunc_sample_result,
                enable_customisable_func=:ALL,
                run_customisable_func_only=true,
            )
        end,
    )
end