build: introduce new Build-SPMProject function

Begin laying out the infrastructure to build SPM based projects.
Certain higher level tools (e.g. swift-inspect, swift-format) do not
have CMake based build systems.  This will allow us to build and package
them as part of the toolchain distribution by building them with SPM
with the partially staged toolchain.

Author: compnerd

build.ps1

@@ -475,6 +475,58 @@ function Build-CMakeProject {
   }
 }
 
+function Build-SPMProject {
+  [CmdletBinding(PositionalBinding = $false)]
+  param(
+    [string] $Src,
+    [string] $Bin,
+    [hashtable] $Arch,
+    [Parameter(ValueFromRemainingArguments)]
+    [string[]] $AdditionalArguments
+  )
+
+  if ($ToBatch) {
+    Write-Output ""
+    Write-Output "echo Building '$Src' to '$Bin' for arch '$($Arch.ShortName)'..."
+  } else {
+    Write-Host -ForegroundColor Cyan "[$([DateTime]::Now.ToString("yyyy-MM-dd HH:mm:ss"))] Building '$Src' to '$Bin' for arch '$($Arch.ShortName)'..."
+  }
+
+  $Stopwatch = [Diagnostics.Stopwatch]::StartNew()
+
+  Isolate-EnvVars {
+    $env:Path = "${RuntimeInstallRoot}\usr\bin;${ToolchainInstallRoot}\usr\bin;${env:Path}"
+    $env:SDKROOT = $Arch.SDKInstallRoot
+
+    $Arguments = @(
+        "--scratch-path", $Bin,
+        "--package-path", $Src,
+        "-c", "release",
+        "-Xbuild-tools-swiftc", "-I$($HostArch.SDKInstallRoot)\usr\lib\swift",
+        "-Xbuild-tools-swiftc", "-L$($HostArch.SDKInstallRoot)\usr\lib\swift\windows",
+        "-Xcc", "-I$($HostArch.SDKInstallRoot)\usr\lib\swift",
+        "-Xlinker", "-L$($HostArch.SDKInstallRoot)\usr\lib\swift\windows"
+    )
+    if ($BuildType -eq "Release") {
+      $Arguments += @("-Xswiftc", "-gnone")
+    } else {
+      if ($SwiftDebugFormat -eq "dwarf") {
+        $Arguments += @("-Xlinker", "-debug:dwarf")
+      } else {
+        $Arguments += @("-g", "-debug-info-format=codeview")
+        $Arguments += @("-Xlinker", "-debug")
+      }
+    }
+
+    Invoke-Program "$($Arch.ToolchainInstallRoot)\usr\bin\swift.exe" "build" @Arguments @AdditionalArguments
+  }
+
+  if (-not $ToBatch) {
+    Write-Host -ForegroundColor Cyan "[$([DateTime]::Now.ToString("yyyy-MM-dd HH:mm:ss"))] Finished building '$Src' to '$Bin' for arch '$($Arch.ShortName)' in $($Stopwatch.Elapsed)"
+    Write-Host ""
+  }
+}
+
 function Build-WiXProject() {
   [CmdletBinding(PositionalBinding = $false)]
   param(