THREAD_ABORT not properly set

[manfred-brands]

This was detected when backporting this to 3.13-dev.

As part of #3984 the following line was replaced in Directory.Build.props

<DefineConstants Condition="'$(TargetFramework)' != 'netstandard2.0'
                            and '$(TargetFramework)' != 'netcoreapp2.1'
                            and '$(TargetFramework)' != 'netcoreapp3.1'
                            and '$(TargetFramework)' != 'net5.0'
                            and '$(TargetFramework)' != 'net5.0-windows'">$(DefineConstants);THREAD_ABORT</DefineConstants>

With:

 <DefineConstants Condition="'$(TargetFrameworkIdentifier)' == '.NETFramework'">$(DefineConstants);THREAD_ABORT</DefineConstants>

Unfortunately TargetFrameworkIdentifier is not yet set when Directory.Build.props is parsed, but only later in Microsoft.NET.TargetFrameworkInference.targets

Then net effect is that THREAD_ABORT is never set.
This is not detected by unit test because we don't test Thread.Abort unless the symbol is set.