Detect outdated/problematic build configurations

[rolfbjarne]

Customers very often have project files with a number of properties that are not in use anymore, or directly conflict with CoreCLR.

For example, the RunAotCompilation property is only applicable when using MonoMV, and will apparently break/confuse a build using CoreCLR.

Android has a build target named _CheckNonIdealConfigurations which will issue warnings if problems are found with a build configuration.

I suggest we add something similar. In some cases we know won't work (RunAotCompilation+CoreCLR) we might just show an error instead, which will likely be more helpful than the confused build error that happens later (or even worse: a successful, but broken, build).

Properties to handle

Properties	Action	Message
RunAotCompilation=true + UseMonoRuntime=false	Error
EnableSGenConc=true + UseMonoRuntime=false	Warning	EnableSGenConc has no effect with CoreCLR
UseInterpreter=true + UseMonoRuntime=false	Warning	UseInterpreter has no effect with CoreCLR
MtouchInterpreter + UseMonoRuntime=false	Warning	MtouchInterpreter has no effect with CoreCLR
MtouchUseLlvm + UseMonoRuntime=false	Warning	MtouchUseLlvm has no effect with CoreCLR