Fix the cross-compiling Windows ARM64 build.

Fix the path to use the build arch instead of the host arch when invoking the built swift compiler. This fixes the build failure that's currently worked around with extra path setting. Cherrypick commit a079beb

Author: hjyamauchi

utils/build.ps1

@@ -866,7 +866,7 @@ function Build-CMakeProject {
  }
 
  if ($UseBuiltCompilers.Contains("Swift")) {
- $env:Path = "$($HostArch.SDKInstallRoot)\usr\bin;$($HostArch.BinaryCache)\cmark-gfm-0.29.0.gfm.13\src;$($HostArch.ToolchainInstallRoot)\usr\bin;${env:Path}"
+ $env:Path = "$($BuildArch.SDKInstallRoot)\usr\bin;$($BuildArch.BinaryCache)\cmark-gfm-0.29.0.gfm.13\src;$($BuildArch.ToolchainInstallRoot)\usr\bin;${env:Path}"
  } elseif ($UsePinnedCompilers.Contains("Swift")) {
  $env:Path = "$(Get-PinnedToolchainRuntime);${env:Path}"
  }