utils: enable the early swift-driver for Windows

Enable the use of the early swift-driver to build the Swift toolchain.
This is the first step towards removing the accumulated debt and
workarounds when building the toolchain on Windows.

Author: compnerd

utils/build.ps1

@@ -1716,9 +1716,6 @@ function Build-CMakeProject {
           Add-KeyValueIfNew $Defines CMAKE_Swift_COMPILER $SWIFTC
           Add-KeyValueIfNew $Defines CMAKE_Swift_COMPILER_TARGET $Platform.Triple
 
-          # TODO(compnerd): remove this once we have the early swift-driver
-          Add-KeyValueIfNew $Defines CMAKE_Swift_COMPILER_USE_OLD_DRIVER "YES"
-
           [string[]] $SwiftFlags = @();
 
           $SwiftFlags += if ($SwiftSDK) {
@@ -1835,9 +1832,6 @@ function Build-CMakeProject {
           Add-KeyValueIfNew $Defines CMAKE_Swift_COMPILER $SWIFTC
           Add-KeyValueIfNew $Defines CMAKE_Swift_COMPILER_TARGET $Platform.Triple
 
-          # TODO(compnerd) remove this once we have the early swift-driver
-          Add-KeyValueIfNew $Defines CMAKE_Swift_COMPILER_USE_OLD_DRIVER "YES"
-
           [string[]] $SwiftFlags = @()
 
           $SwiftFlags += if ($SwiftSDK) {
@@ -2292,6 +2286,7 @@ function Get-CompilersDefines([Hashtable] $Platform, [string] $Variant, [switch]
     SWIFT_TOOLCHAIN_VERSION = "${ToolchainIdentifier}";
     SWIFT_BUILD_SWIFT_SYNTAX = "YES";
     SWIFT_CLANG_LOCATION = (Get-PinnedToolchainToolsDir);
+    SWIFT_EARLY_SWIFT_DRIVER_BUILD = "$(Get-ProjectBinaryCache $BuildPlatform EarlySwiftDriver)\bin";
     SWIFT_ENABLE_EXPERIMENTAL_CONCURRENCY = "YES";
     SWIFT_ENABLE_EXPERIMENTAL_CXX_INTEROP = "YES";
     SWIFT_ENABLE_EXPERIMENTAL_DIFFERENTIABLE_PROGRAMMING = "YES";