Obsolete warnings on clean build

[ericstj]

Initial cost estimate: 2 days
Initial contacts: @trylek, @ViktorHofer

#39269 introduced warnings to the full build.

For example https://dev.azure.com/dnceng/public/_build/results?buildId=746713&view=results

Shows 18 warnings which seem to be test code:

LowLatencyTest.cs(111,13): warning SYSLIB0004: 'RuntimeHelpers.PrepareConstrainedRegions()' is obsolete: 'The Constrained Execution Region (CER) feature is not supported.'
CoreCLR Common Pri0 Test Build AnyOS AnyCPU checked • Build managed test components
TestInALC.cs(13,77): warning SYSLIB0012: 'Assembly.CodeBase' is obsolete: 'CodeBase and EscapedCodeBase are only included for .NET Framework compatibility. Use Location instead.'
CoreCLR Common Pri0 Test Build AnyOS AnyCPU checked • Build managed test components
RunInALC.cs(42,73): warning SYSLIB0012: 'Assembly.CodeBase' is obsolete: 'CodeBase and EscapedCodeBase are only included for .NET Framework compatibility. Use Location instead.'
CoreCLR Common Pri0 Test Build AnyOS AnyCPU checked • Build managed test components
TestInALC.cs(13,77): warning SYSLIB0012: 'Assembly.CodeBase' is obsolete: 'CodeBase and EscapedCodeBase are only included for .NET Framework compatibility. Use Location instead.'
CoreCLR Common Pri0 Test Build AnyOS AnyCPU checked • Build managed test components
TestInALC.cs(13,77): warning SYSLIB0012: 'Assembly.CodeBase' is obsolete: 'CodeBase and EscapedCodeBase are only included for .NET Framework compatibility. Use Location instead.'
CoreCLR Common Pri0 Test Build AnyOS AnyCPU checked • Build managed test components
GitHub_25468.cs(82,9): warning SYSLIB0011: 'BinaryFormatter.Serialize(Stream, object)' is obsolete: 'BinaryFormatter serialization is obsolete and should not be used. See https://aka.ms/binaryformatter for more information.'
CoreCLR Common Pri0 Test Build AnyOS AnyCPU checked • Build managed test components
GitHub_25468.cs(85,24): warning SYSLIB0011: 'BinaryFormatter.Deserialize(Stream)' is obsolete: 'BinaryFormatter serialization is obsolete and should not be used. See https://aka.ms/binaryformatter for more information.'
CoreCLR Common Pri0 Test Build AnyOS AnyCPU checked • Build managed test components
test22888.cs(68,73): warning SYSLIB0012: 'Assembly.CodeBase' is obsolete: 'CodeBase and EscapedCodeBase are only included for .NET Framework compatibility. Use Location instead.'
CoreCLR Common Pri0 Test Build AnyOS AnyCPU checked • Build managed test components 
IpcUtils.cs(73,55): warning SYSLIB0012: 'Assembly.CodeBase' is obsolete: 'CodeBase and EscapedCodeBase are only included for .NET Framework compatibility. Use Location instead.'
CoreCLR Common Pri0 Test Build AnyOS AnyCPU checked • Build managed test components
LowLatencyTest.cs(111,13): warning SYSLIB0004: 'RuntimeHelpers.PrepareConstrainedRegions()' is obsolete: 'The Constrained Execution Region (CER) feature is not supported.' Mono Common Pri0 Test Build AnyOS AnyCPU release • Build managed test components
TestInALC.cs(13,77): warning SYSLIB0012: 'Assembly.CodeBase' is obsolete: 'CodeBase and EscapedCodeBase are only included for .NET Framework compatibility. Use Location instead.' Mono Common Pri0 Test Build AnyOS AnyCPU release • Build managed test components
RunInALC.cs(42,73): warning SYSLIB0012: 'Assembly.CodeBase' is obsolete: 'CodeBase and EscapedCodeBase are only included for .NET Framework compatibility. Use Location instead.' Mono Common Pri0 Test Build AnyOS AnyCPU release • Build managed test components
TestInALC.cs(13,77): warning SYSLIB0012: 'Assembly.CodeBase' is obsolete: 'CodeBase and EscapedCodeBase are only included for .NET Framework compatibility. Use Location instead.' Mono Common Pri0 Test Build AnyOS AnyCPU release • Build managed test components
TestInALC.cs(13,77): warning SYSLIB0012: 'Assembly.CodeBase' is obsolete: 'CodeBase and EscapedCodeBase are only included for .NET Framework compatibility. Use Location instead.' Mono Common Pri0 Test Build AnyOS AnyCPU release • Build managed test components
GitHub_25468.cs(82,9): warning SYSLIB0011: 'BinaryFormatter.Serialize(Stream, object)' is obsolete: 'BinaryFormatter serialization is obsolete and should not be used. See https://aka.ms/binaryformatter for more information.' Mono Common Pri0 Test Build AnyOS AnyCPU release • Build managed test components
GitHub_25468.cs(85,24): warning SYSLIB0011: 'BinaryFormatter.Deserialize(Stream)' is obsolete: 'BinaryFormatter serialization is obsolete and should not be used. See https://aka.ms/binaryformatter for more information.' Mono Common Pri0 Test Build AnyOS AnyCPU release • Build managed test components
test22888.cs(68,73): warning SYSLIB0012: 'Assembly.CodeBase' is obsolete: 'CodeBase and EscapedCodeBase are only included for .NET Framework compatibility. Use Location instead.' Mono Common Pri0 Test Build AnyOS AnyCPU release • Build managed test components
IpcUtils.cs(73,55): warning SYSLIB0012: 'Assembly.CodeBase' is obsolete: 'CodeBase and EscapedCodeBase are only included for .NET Framework compatibility. Use Location instead.' Mono Common Pri0 Test Build AnyOS AnyCPU release • Build managed test components

cc @jeffhandley

[danmoseley]

@jkoritzinsky these aside, should warnings be treated as errors in the Clr tests (and all other code we have)? Then presumably this would have been found in PR validation.

[jkoritzinsky]

Traditionally we havent done warnings-as-errors for the CLR tests because we always had a ton of warnings due to the weird build setup. It would be worth investigating if we can enable warn-as-error for the CLR test build.

[danmoseley]

Compiler warnings, or MSBuild warnings? The former should be suppressible, if expected, of course.