On Linux, a folder with a backslash results in MSB3552 for resource files

### Steps to reproduce
```
$ dotnet new console
$ mkdir dir\\name
$ dotnet build
```
Note that the second command creates a folder that contains a literal backslash in its name. By accident, I had created a folder named `C:\Users\Jane\Desktop` on my Linux box.

### Expected behavior
The build should work

### Actual behavior
The build fails with
```
/usr/share/dotnet/sdk/2.1.403/Microsoft.Common.CurrentVersion.targets(3049,5): error MSB3552: Resource file "**/*.resx" cannot be found. […/dotnettest.csproj]
```

### Environment data
dotnet 2.1.403