NETCOREAPP3_1 is declared in .NET 5.0 RC1

[virzak]

Description

When running this code using .NET 5, the expectation is that it will compile, but it doesn't:

using System;

namespace MacroBug
{
    public class Class1
    {

#if NETCOREAPP3_1
NETCOREAPP3_1 Here to break Compilation
#endif

#if NETCOREAPP3_0
NETCOREAPP3_0 Here to break Compilation
#endif

#if !NET5_0
!NET5_0 Here to break Compilation
#endif
        
    }
}

Configuration

.NET 5.0 RC 1 (5.0.100-rc.1.20452.10) on Windows 10 x64

Other information

NETCOREAPP3_0 works as expected (not declared in .NET 5)

[ghost]

Tagging subscribers to this area: @dotnet/ncl
See info in area-owners.md if you want to be subscribed.

[stephentoub]

Thanks. Dup of dotnet/sdk#13377. See dotnet/docs#20692.