utils: correct the host that we reference for the tools

We need to use the build for the tools rather than the host. This is to
help fix the cross-compilation scenarios.

Author: compnerd

utils/build.ps1

@@ -1536,9 +1536,9 @@ function Build-SPMProject {
   $Stopwatch = [Diagnostics.Stopwatch]::StartNew()
 
   Invoke-IsolatingEnvVars {
-    $RuntimeInstallRoot = [IO.Path]::Combine((Get-InstallDir $HostPlatform), "Runtimes", $ProductVersion)
+    $RuntimeInstallRoot = [IO.Path]::Combine((Get-InstallDir $BuildPlatform), "Runtimes", $ProductVersion)
 
-    $env:Path = "$RuntimeInstallRoot\usr\bin;$($HostPlatform.ToolchainInstallRoot)\usr\bin;${env:Path}"
+    $env:Path = "$RuntimeInstallRoot\usr\bin;$($BuildPlatform.ToolchainInstallRoot)\usr\bin;${env:Path}"
     $env:SDKROOT = (Get-SwiftSDK Windows)
     $env:SWIFTCI_USE_LOCAL_DEPS = "1"
 
@@ -1574,7 +1574,7 @@ function Build-SPMProject {
       }
     }
 
-    Invoke-Program "$($HostPlatform.ToolchainInstallRoot)\usr\bin\swift.exe" $ActionName @Arguments @AdditionalArguments
+    Invoke-Program "$($BuildPlatform.ToolchainInstallRoot)\usr\bin\swift.exe" $ActionName @Arguments @AdditionalArguments
   }
 
   if (-not $ToBatch) {