They were building as 64-bit only since there wasn't a 32-bit CoreCLR before.

This should either be defined globally or not at all.  Repeating all the logic on a local level is just wasted time.

TLDR: artifacts are going to move around in Binaries\Debug and the directory is going to get a lot bigger.

At a high level build projects can be classified into three categories based on how they write output:

- incorrect: a given output path is written to more than once with different contents
- less correct: a given output path is written to more than once but always with the same content
- correct: a given output path is written to exactly once

Today the roslyn build is decidedly “incorrect” as pretty much every file is written directly into Binaries\Debug. This means it ends up writing pretty much every Visual Studio SDK DLL twice: once for Dev14 and once for Dev15. For example at various points in the build Binaries\Debug\Microsoft.VisualStudio.Text.Data.dll may refer to Dev14 and at others it’s Dev15. If this seems like a scary proposition for a build that’s because it is indeed scary and it has real consequences. By now pretty much everyone on the team has hit the build race condition that is dragging down our PRs.

The general fix here is to move build outputs into separate directories. Instead of building to $(Configuration) projects now build into say $(Configuration)\Exes\$(MSBuildProjectFileName). This will have a substantial increase in the size of Binaries. We will be looking into ways to reduce that. In the short term though build stability far outweighs the size increase.

This change takes us most of the way to "correct". There are several places I had to compromise in order to get this initial change in:

- UnitTests still build to a common output folder (one for Dev14, another for Dev15). Pulling unit tests apart is going to take a bit of work.
- Every project has a <RoslynProjectType> entry. This will go away in the future for most projects. It's temporarily needed so I can fix roslyn-internal in parallel without taking down the build.
- VSL.Imports.targets is messy. Unavoidable for now due to the above. It will get cleaner as I iterate on this.

None of these are relevant to the underlying race condition. Hence it's okay to push them off.

The ImportGroup element is just noise.  It was also used very inconsistently in the repo and often within the same project file.  Just remove it.

This reverts commit 760e1204.

Fixes - #8951

This reverts commit e2fc5135.

Synchronize all corefx references to -23504 and bring in the
xunit coreclr test runner.

by removing `<DebugType>` lines from projects that import `VSL.Settings.targets`

This changes BuildClient and it's derived types to make it possible to
host compilations in process.  Previously the client had hard coded
references to Console.Out which prevented this from happening.  Now it
is threaded through as a parameter that can be controlled by test code.

The rsp files aren't useful because there are no automatic references
when running on coreclr. The exe.config files aren't useful because
there are no binding redirects on coreclr.

Resolves #4101.

The intent of the code base was to be run with overflow checking disabled.  However the actual settings were quite a bit different:

- CSharp: checking enabled in debug, disabled in release
- VB: checking disabled in all modes

For both languages individual projects could, and often did, override this setting.  Typically it specified the global default but not always.

This is confusing and makes it difficult to reason about our source code.  Furthermore much of our testing occurs in debug mode and it's not logical for our code to behave substantially different in Debug than it would in Release.

This change clarifies our overflow checking behavior.  It's disabled in all modes now.  The change goes further to prevent individual projects from overriding this setting and adds unit tests to make sure it was applied correctly.

Note: this PR is not intended to state whether it's better for overflow checking to be enabled or disabled.  It is intended to enforce the decision the code base was designed around.

This is a more appropriate place for the type.

Simplify the client build by moving to a root type with a desktop and
portable variation.  This allows us to share more infrastructure between
the layers.

Move the majority of the build logic to a shared project.

This doesn't completely work yet because ServerCore can't reference this
(it's a 4.5 portable project).  I need to remove the dependency on it
here and move the dependency out to VBCSCompiler.

Fixes: #6423

Object Browser was forcing compilations to be realized just to compute the assembly identity for each of a compilation's metadata references. With this change, the Object Browser will use the metadata references from the project and call the same utility function that is used to read assembly identity for analyzer assemblies.

Move the files in the compiler that are shared by source with other projects into the Shared folder.  This combined files which weren't in a shared location and those previously in Helpers.