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

@@ -1867,6 +1867,7 @@ 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";