[Windows] Prepare for swift-foundation in the toolchain (#74127)

* [Windows] Prepare for swift-foundation in the toolchain

* Update SwiftSyntax directory

Author: jmschonfeld

utils/build.ps1

@@ -1629,6 +1629,7 @@ function Build-Dispatch([Platform]$Platform, $Arch, [switch]$Test = $false) {
 
 function Build-Foundation([Platform]$Platform, $Arch, [switch]$Test = $false) {
   $DispatchBinaryCache = Get-TargetProjectBinaryCache $Arch Dispatch
+  $SwiftSyntaxDir = Get-HostProjectCMakeModules Compilers
   $FoundationBinaryCache = Get-TargetProjectBinaryCache $Arch Foundation
   $ShortArch = $Arch.LLVMName
 
@@ -1695,6 +1696,10 @@ function Build-Foundation([Platform]$Platform, $Arch, [switch]$Test = $false) {
         };
         ZLIB_INCLUDE_DIR = "$LibraryRoot\zlib-1.3.1\usr\include";
         dispatch_DIR = "$DispatchBinaryCache\cmake\modules";
+        SwiftSyntax_DIR = "$SwiftSyntaxDir";
+        _SwiftFoundation_SourceDIR = "$SourceCache\swift-foundation";
+        _SwiftFoundationICU_SourceDIR = "$SourceCache\swift-foundation-icu";
+        _SwiftCollections_SourceDIR = "$SourceCache\swift-collections"
       } + $TestingDefines)
   }
 }