Add libdispatch WoA detection until merged

swiftlang/swift-corelibs-libdispatch#803

Author: hmelder

patches/libdispatch-fix-woa-detection.patch

@@ -0,0 +1,15 @@
+https://github.com/apple/swift-corelibs-libdispatch/pull/803
+---
+diff --git a/cmake/modules/DispatchWindowsSupport.cmake b/cmake/modules/DispatchWindowsSupport.cmake
+index 87675a7..750b3be 100644
+--- a/cmake/modules/DispatchWindowsSupport.cmake
++++ b/cmake/modules/DispatchWindowsSupport.cmake
+@@ -6,7 +6,7 @@ function(dispatch_windows_arch_spelling arch var)
+     set(${var} x64 PARENT_SCOPE)
+   elseif(${arch} STREQUAL armv7)
+     set(${var} arm PARENT_SCOPE)
+-  elseif(${arch} STREQUAL aarch64)
++  elseif(${arch} STREQUAL aarch64 OR ${arch} STREQUAL ARM64)
+     set(${var} arm64 PARENT_SCOPE)
+   else()
+     message(FATAL_ERROR "do not know MSVC spelling for ARCH: `${arch}`")