When UTF-8 is the system default codepage, the encoding we get is
`Encoding.UTF8`, which uses a BOM. Unfortunately, `cmd.exe` emits an
error when trying to execute a file that starts with a BOM, so all Exec
tasks on an OS with that configuration are broken.

Instead, if the default encoding is a UTF-8 variant with a BOM, force it
to use UTF-8 with no BOM.

This is convoluted because MSBuildTaskHost isn't built all the time:
since it targets .NET 3.5, it can only be built from full framework
MSBuild. So introduce a new define to conditionalize the test.

`CancelledBuildInTaskHostWithDelay20` was running the MSBuild 3.5
version of the Exec task in a TaskHost, but the TaskHost in question
used the 4.0 runtime, so it ran in a copy of MSBuild.exe.

This didn't exercise the more-interesting pathway of running the
legacy task in the legacy-compat environment in MSBuildTaskHost.exe.

update

Preserve edges from graph construction in order to retrieve ProjectReferenceItem.Targets at target computation time.

Co-Authored-By: Rainer Sigwald <raines@microsoft.com>

This is a very slight optimization, as string.equals checks that lengths are equal before comparing characters.

Another very slight optimization. Checking this first eliminates a reasonable number of allocations done by GetDirectoryName. Can be further optimized.

…h a slash

Also fixed issue with IsDrivePatternWithSlash accessing an out of bounds index. Forgot parantheses (whoops)

Can be improved by further investigating edge cases that Path.GetDirectoryName returns null in.

Fixes dotnet#4547 by respecting the Implementation metadata only when it's a .dll. The <16.2.0 behavior would only find a .dll, and the comment on ImplementationAssembly expects it to always be a .dll, so I think this is reasonable.

* Update dependencies from https://github.com/dotnet/arcade build 20190723.6

- Microsoft.DotNet.Arcade.Sdk - 1.0.0-beta.19373.6

* Update dependencies from https://github.com/dotnet/arcade build 20190724.2

- Microsoft.DotNet.Arcade.Sdk - 1.0.0-beta.19374.2

* Update dependencies from https://github.com/dotnet/arcade build 20190725.2

- Microsoft.DotNet.Arcade.Sdk - 1.0.0-beta.19375.2

…otnet#4544)

This test was disabled long ago but appears to be fine now, presumably due to CoreFX updates.

Fixes dotnet#301.

)

This reverts commit ea574a4.

Fixes dotnet#234.

WinRT: Accept Implementation metadata only when it's a DLL

…726.18

- Microsoft.DotNet.Arcade.Sdk - 1.0.0-beta.19376.18

…a3-4e7a-9a9b-c92457bc2288

[master] Update dependencies from dotnet/arcade

.. copied to the bindir.

This had to be cobbled together manually, as the build details changed
upstream.

Branch:     `dotnet/toolset` - `release/3.0.100-preview8`
HEAD:       9c8c1c8

Microsoft.NET.Sdk:                          3.0.100-preview8.19406.1
Microsoft.NET.Build.Extensions:             3.0.100-preview8.19406.1

Microsoft.NET.Sdk.Web:                      3.0.100-preview8.19406.4
Microsoft.NET.Sdk.Publish:                  3.0.100-preview8.19406.4
Microsoft.NET.Sdk.Web.ProjectSystem:        3.0.100-preview8.19406.4

Microsoft.NET.Sdk.Razor:                    3.0.0-preview8.19405.5

ILLink.Tasks:                               0.1.6-prerelease.19379.2

NuGet.Build.Tasks*:                         5.3.0-preview.2.6136

libhostfxr.dylib:                           3.0.100-preview8-013422
	- copied from `dotnet`, installed with `./eng/common/dotnet-install.sh -v 3.0.100-preview8-013422`

Microsoft.DotNet.MSBuildSdkResolver:        3.0.100-preview8.19406.4
	- version from `core-sdk` repo's HEAD
		https://github.com/dotnet/core-sdk/blob/8bf06ffc8d99abcc7c8a923e90b35d122887976d/eng/Versions.props#L36
	- on suggestion from Livar Cunha .

Versions from https://github.com/dotnet/toolset/blob/9c8c1c85d181cde1d7c43180c4072ce4c2f54adb/eng/Versions.props

.. as required.

.. update-sdks-roslyn-2019-06 .