Avoid SourceLink in bootstrap Core build

SourceLink is a fancy modern package with fancy new MSBuild syntax . . .
which breaks on the ancient copy of MSBuild we use to bootstrap for
CoreCLR. Just don't SourceLink in that phase.

cibuild.cmd

@@ -80,6 +80,9 @@ set RUNTIME_HOST=
 if /i "%HOST%"=="CoreCLR" (
     set RUNTIME_HOST=%~dp0Tools\DotNetCLI\Dotnet.exe
     set MSBUILD_CUSTOM_PATH=%~dp0Tools\MSBuild.exe
+    :: The LKG MSBuild on Core is too old to support
+    :: SourceLink targets, so disable them.
+    set SOURCE_LINK_ARGUMENT=/p:SourceLinkCreate=false
 ) else if /i "%HOST%"=="Full" (
     set RUNTIME_HOST=
 ) else (
@@ -104,7 +107,7 @@ echo.
 echo ** Rebuilding MSBuild with downloaded binaries
 
 set MSBUILDLOGPATH=%~dp0msbuild_bootstrap_build-%HOST%.log
-call "%~dp0build.cmd" /t:Rebuild /p:Configuration=%BUILD_CONFIGURATION% /p:"SkipBuildPackages=true" %LOCALIZED_BUILD_ARGUMENT% %SYNC_XLF_ARGUMENT% %RUNTIMETYPE_ARGUMENT%
+call "%~dp0build.cmd" /t:Rebuild /p:Configuration=%BUILD_CONFIGURATION% /p:"SkipBuildPackages=true" %LOCALIZED_BUILD_ARGUMENT% %SYNC_XLF_ARGUMENT% %RUNTIMETYPE_ARGUMENT% %SOURCE_LINK_ARGUMENT%
 
 if %ERRORLEVEL% NEQ 0 (
     echo.

cibuild.sh

@@ -322,7 +322,8 @@ restoreBuildTools
 
 echo
 echo "** Rebuilding MSBuild with downloaded binaries"
-runMSBuildWith "$RUNTIME_HOST" "$RUNTIME_HOST_ARGS" "$MSBUILD_EXE" "/t:Rebuild $BUILD_MSBUILD_ARGS $CSC_ARGS" "$BOOTSTRAP_BUILD_LOG_PATH"
+# Avoid SourceLink on our ancient bootstrap binaries
+runMSBuildWith "$RUNTIME_HOST" "$RUNTIME_HOST_ARGS" "$MSBUILD_EXE" "/t:Rebuild $BUILD_MSBUILD_ARGS $CSC_ARGS /p:SourceLinkCreate=false /p:DebugType=portable" "$BOOTSTRAP_BUILD_LOG_PATH"
 
 if [[ $BUILD_ONLY = true ]]; then
     exit $?

dir.targets

@@ -55,6 +55,9 @@
           Condition="'$(CopyBuildOutputToDeploymentDirectories)' != 'false'">
     <ItemGroup>
       <OutputItems Include="$(OutputPath)\**\*.*"/>
+
+      <!-- Avoid race condition between project's IncrementalClean coming along to delete the .pdb and this project copying it. -->
+      <OutputItems Remove="$(OutputPath)\**\*.pdb" Condition="'$(DebugType)' == 'embedded'" />
     </ItemGroup>
 
     <Copy SourceFiles="@(OutputItems)"

src/dir.targets

@@ -107,7 +107,7 @@
 
   <!-- https://github.com/ctaggart/SourceLink - stamps portable or embedded .pdbs with URLs to sources on GitHub
        so that debugger can download the exact matching source files during debugging -->
-  <Import Project="$(PackagesDir)\sourcelink.create.commandline\2.1.2\build\SourceLink.Create.CommandLine.targets" Condition="'$(DebugType)' != 'full' And '$(IsTestProject)' != 'true' And Exists('$(PackagesDir)\sourcelink.create.commandline\2.1.2\build\SourceLink.Create.CommandLine.targets')" />
+  <Import Project="$(PackagesDir)\sourcelink.create.commandline\2.1.2\build\SourceLink.Create.CommandLine.targets" Condition="'$(SourceLinkCreate)' == 'true' And '$(DebugType)' != 'full' And '$(IsTestProject)' != 'true' And Exists('$(PackagesDir)\sourcelink.create.commandline\2.1.2\build\SourceLink.Create.CommandLine.targets')" />
 
 
   <!-- Taken from Microsoft.VisualStudio.SDK.EmbedInteropTypes NuGet package which tries to fix this issue