Create build-windows-toolchain.bat

Author: shahmishal

utils/build-windows-toolchain.bat

@@ -0,0 +1,10 @@
+:: build-windows-toolchain.bat
+::
+:: This source file is part of the Swift.org open source project
+::
+:: Copyright (c) 2014 - 2021 Apple Inc. and the Swift project authors
+:: Licensed under Apache License v2.0 with Runtime Library Exception
+::
+:: See https://swift.org/LICENSE.txt for license information
+:: See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+