Copy GC settings from host process

[adamsitnik]

We have been always recognizing the settings of the Host process:

BenchmarkDotNet/src/BenchmarkDotNet/Environments/GcResolver.cs

Lines 12 to 13 in 4bd433d

	Register(GcMode.ServerCharacteristic, () => HostEnvironmentInfo.GetCurrent().IsServerGC);
	Register(GcMode.ConcurrentCharacteristic, () => HostEnvironmentInfo.GetCurrent().IsConcurrentGC);

But for some reason we have never re-applied them to benchmark process. Which could cause a confusion in cases where users apply things like:

<ServerGarbageCollection>true</ServerGarbageCollection>

in their project file.

Reported offline by @stephentoub

[stephentoub]

Thanks :)