utils: add support for testing self-hosted SPM

`-Test swiftpm` will use the self-hosted build of SPM to run the test
suite. By using the `SWIFTCI_USE_LOCAL_DEPS=1` environment variable, we
do reduce some of the cost of this by not recloning the repositories,
but the entire dependency tree must be built a second time due to the
switch in the build system.

Author: compnerd

utils/build.ps1

@@ -768,6 +768,7 @@ function Build-SPMProject {
     [string] $Src,
     [string] $Bin,
     [hashtable] $Arch,
+    [switch] $Test = $false,
     [Parameter(ValueFromRemainingArguments)]
     [string[]] $AdditionalArguments
   )
@@ -804,7 +805,8 @@ function Build-SPMProject {
       $Arguments += @("-debug-info-format", "none")
     }
 
-    Invoke-Program "$ToolchainInstallRoot\usr\bin\swift.exe" "build" @Arguments @AdditionalArguments
+    $Action = if ($Test) { "test" } else { "build" }
+    Invoke-Program "$ToolchainInstallRoot\usr\bin\swift.exe" $Action @Arguments @AdditionalArguments
   }
 
   if (-not $ToBatch) {
@@ -1728,6 +1730,20 @@ function Build-DocC() {
   }
 }
 
+function Test-PackageManager() {
+  $OutDir = Join-Path -Path $HostArch.BinaryCache -ChildPath swift-package-manager
+
+  Isolate-EnvVars {
+    $env:SWIFTCI_USE_LOCAL_DEPS=1
+    Build-SPMProject `
+      -Test `
+      -Src $SourceCache\swift-package-manager `
+      -Bin $OutDir `
+      -Arch $HostArch `
+      -Xcc -Xclang -Xcc -fno-split-cold-code -Xcc "-I$LibraryRoot\sqlite-3.43.2\usr\include" -Xlinker "-L$LibraryRoot\sqlite-3.43.2\usr\lib"
+  }
+}
+
 function Build-Installer($Arch) {
   $Properties = @{
     BundleFlavor = "offline";
@@ -1875,6 +1891,7 @@ if ($Test -contains "dispatch") { Build-Dispatch $HostArch -Test }
 if ($Test -contains "foundation") { Build-Foundation $HostArch -Test }
 if ($Test -contains "xctest") { Build-XCTest $HostArch -Test }
 if ($Test -contains "llbuild") { Build-LLBuild $HostArch -Test }
+if ($Test -contains "swiftpm") { Test-PackageManager $HostArch }
 
 # Custom exception printing for more detailed exception information
 } catch {