.NETCoreApp,Version=v2.1.AssemblyAttributes.fs is stored in global /tmp on Linux

Please provide a succinct description of the issue.

The file `.NETCoreApp,Version=v2.1.AssemblyAttributes.fs` is created and stored in `/tmp` on Linux. This is a problem in multi-user environments (e.g., a CS UNIX lab) because only one student at a time can work with F#.

It is not totally clear to me whether this is a problem with the F# compiler or `dotnet`, but my money is on the compiler given that the file ends in `.fs`.

#### Repro steps

Provide the steps required to reproduce the problem

1. As user A, run `dotnet new console -lang F#`.
2. `dotnet build` as user A.
3. As user B, run `dotnet new console -lang F#`.
4. `dotnet build` as user B.

#### Expected behavior

Compile should succeed.

#### Actual behavior

`FSC : error FS0193: Access to the path '/tmp/.NETCoreApp,Version=v2.1.AssemblyAttributes.fs' is denied. [/whatever/test/test.fsproj]`

#### Known workarounds

The only workaround I know of at present is to make students use different machines. This is a little problematic since we encourage them to SSH into our lab machines.

#### Related information

```
$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 16.04.3 LTS
Release: 16.04
Codename: xenial
```
```
$ dotnet --version
2.1.402
```

```
$ fsharpc
F# Compiler for F# 4.0 (Open Source Edition)
Freely distributed under the Apache 2.0 Open Source License
```

Severity: this makes F# pretty difficult to use as a teaching tool. I replaced SML with F# in our PL course... hopefully we can resolve this.