runtime: System.Numerics.Vectors partialfacades error: Invalid local constant signature: 'epsilon'

1. Run build.cmd on a clean clone of the repo.
2. Observe partialfacade errors.

This issue might have been exposed by recent buildtools changes, specifically https://github.com/dotnet/buildtools/pull/2038, but I am not sure.

Looking at the list of recent commits to master, the corefx repo builds successfully from yesterday’s last commit, prior to the dependencies update: aa73b08881ccc2a438947c19d60a6665008bcc08

The error appears after https://github.com/dotnet/corefx/pull/29836 got merged (i.e. e693ef593b152fc9f92049b63afed967f167cf6f).

D:\GitHub\Fork\corefx\Tools\partialfacades.task.targets(64,5): error : PDB0018: token 0x0600001F: Invalid local constant signature: 'epsilon' [D:\GitHub\Fork\corefx\src\System.Numerics.Vectors\src\System.Numerics.Vectors.csproj]
D:\GitHub\Fork\corefx\Tools\partialfacades.task.targets(64,5): error : PDB0018: token 0x06000020: Invalid local constant signature: 'epsilon' [D:\GitHub\Fork\corefx\src\System.Numerics.Vectors\src\System.Numerics.Vectors.csproj]
D:\GitHub\Fork\corefx\Tools\partialfacades.task.targets(64,5): error : PDB0018: token 0x0600003B: Invalid local constant signature: 'epsilon' [D:\GitHub\Fork\corefx\src\System.Numerics.Vectors\src\System.Numerics.Vectors.csproj]
D:\GitHub\Fork\corefx\Tools\partialfacades.task.targets(64,5): error : PDB0018: token 0x0600003C: Invalid local constant signature: 'epsilon' [D:\GitHub\Fork\corefx\src\System.Numerics.Vectors\src\System.Numerics.Vectors.csproj]
D:\GitHub\Fork\corefx\Tools\partialfacades.task.targets(64,5): error : PDB0018: token 0x0600003C: Invalid local constant signature: 'minAngle' [D:\GitHub\Fork\corefx\src\System.Numerics.Vectors\src\System.Numerics.Vectors.csproj]
D:\GitHub\Fork\corefx\Tools\partialfacades.task.targets(64,5): error : PDB0018: token 0x06000059: Invalid local constant signature: 'EPSILON' [D:\GitHub\Fork\corefx\src\System.Numerics.Vectors\src\System.Numerics.Vectors.csproj]
D:\GitHub\Fork\corefx\Tools\partialfacades.task.targets(64,5): error : PDB0018: token 0x06000072: Invalid local constant signature: 'FLT_EPSILON' [D:\GitHub\Fork\corefx\src\System.Numerics.Vectors\src\System.Numerics.Vectors.csproj]
D:\GitHub\Fork\corefx\Tools\partialfacades.task.targets(64,5): error : PDB0018: token 0x0600008B: Invalid local constant signature: 'epsilon' [D:\GitHub\Fork\corefx\src\System.Numerics.Vectors\src\System.Numerics.Vectors.csproj]

cc @eerhardt, @ViktorHofer, @danmosemsft, @stephentoub