build.ps1: enable Foundation tools on experimental SDK

When building the experimental SDK, build the foundation tools. This is
needed to ensure that we can package the runtime without the legacy SDK.

Author: compnerd

utils/build.ps1

@@ -3249,7 +3249,7 @@ function Build-ExperimentalSDK([Hashtable] $Platform) {
           CMAKE_STATIC_LIBRARY_PREFIX_Swift = "lib";
           ENABLE_TESTING = "NO";
 
-          FOUNDATION_BUILD_TOOLS = "NO";
+          FOUNDATION_BUILD_TOOLS = if ($Platform.OS -eq [OS]::Windows) { "YES" } else { "NO" };
           CURL_DIR = "$BinaryCache\$($Platform.Triple)\usr\lib\cmake\CURL";
           LibXml2_DIR = "$BinaryCache\$($Platform.Triple)\usr\lib\cmake\libxml2-2.11.5";
           ZLIB_INCLUDE_DIR = "$BinaryCache\$($Platform.Triple)\usr\include";