…SDK style projects

…rgets} fpr SDK projects

Only pull in the buildtools targets for depproj, ilproj and non-sdk csproj

…x instead

This reverts commit dce8e68.

…utables

… targets for non-sdk projects, and only default to not building sdk projects when we're part of the overall build

….Private.CoreLib

… logic clearer

The generated wrapper needs to target netcoreapp on unix. I had to
exclude assets from the xunit package and introduce a dependency on
the private corefx bits, to resolve a dependency conflict in which the
generated wrapper was depending on an older System.Runtime.dll than
the helper library.

I also disabled binclash logging, because the wrapper build binplaces
the helper library to the same location multiple times. I couldn't
find a simple way to disable binclash logging for the wrapper build
only, since that requires passing an empty switch to run.exe, and bash
word splitting makes this nontrivial from build-test.

Note that this will still require changes to the test wrapper
to actually source the TestEnv on unix

This way, the wrappers can build even if the 2.1 SDK isn't installed on
the machine.

When building wrappers using the SDK, we need some basic
properties (like the build os/arch/config, and the output directories)
to be set. I factored out properties used by both the old test build
and the new SDK-project test build.

At first I tried using Directory.Build.props (which is automatically
imported by the SDK), but our test build already imports SDK targets
in various places, so this was resulting in duplicate
imports. Instead, I used dir.common.props, and made the imports
explicit.

Use bash arrays to pass parameters for the build command. This makes
it possible to pass arguments with spaces to build_Tests_internal. We
use this to disable binclashlogging selectively (for the xunit wrapper
build only).

tests/src/dir.common.props was only used for the desktop-specific
xunit wrapper helper library. There's no need for it any more, so its
properties have been moved into tests/src/dir.props.

dir.sdkbuild.props has been renamed to dir.common.props, since it
contains properties used by SDK projects and buildtools projects.

This change also re-enables the test build.

With this, some properties shared by SDK projects can go in a global
location. The TargetFramework is shared by all SDK projects in the
test tree.

This change also uses a property for the xunit package directory that
contains the xunit.console.dll we copy to core_root.

This fixes a failure in the windows build.

On windows, the use of run.exe, config.json, and msbuild.cmd uses
msbuild.exe on the path. This change will build wrappers using the
local SDK via "dotnet msbuild", bypassing run.exe. Run.exe will go
away entirely with the move from buildtools to arcade, so other build
invocatios should follow suit.

UseBuildTools used to be true all the time. Now that we are building
wrappers on core, UseBuildTools becomes false. However, the rest of
the runtest.proj expects to build using buildtools, so we keep
UseBuildTools true until we switch to arcade.

The CSharpCoreTargetsPath was imported when running on core only. This
used to happen only on unix, but now it also happens when building
runtest.proj for the xunit wrappers on windows. On unix, this targets
file was a symlink to itself to work around some buildtools logic that
expected the file to exist. This workaround no longer appears
necessary, and on windows, this was never used in the first place, so
this change removes it.

UseRoslynCompilers was introduced in buildtools by
dotnet/buildtools#947, with different
behaviors on windows/unix. It was removed by
dotnet/buildtools#1974, so we can unify our
roslyn imports now.

…into merge_sven_xunit

# Conflicts:
#	tests/src/dir.common.props

…_sven_xunit

…rojects

…hem picking up dirs.props/targets automatically