[6.2.1] Add Equatable and Hashable conformance to GUID.

test/stdlib/WinSDK_GUID.swift

@@ -0,0 +1,22 @@
+// RUN: %target-build-swift %s -o %t.exe
+// RUN: %target-codesign %t.exe
+// RUN: %target-run %t.exe
+// REQUIRES: executable_test
+// REQUIRES: OS=windows-msvc
+
+// Make sure that importing WinSDK brings in the GUID type, which is declared in
+// /shared and not in /um.
+
+import WinSDK
+
+public func usesGUID(_ x: GUID) {}
+
+// Make sure equating and hashing GUIDs works.
+
+let guid: GUID = GUID_NULL
+assert(guid == guid)
+assert(guid.hashValue == guid.hashValue)
+
+let guid2: GUID = IID_IUnknown
+assert(guid != guid2)
+assert(guid.hashValue != guid2.hashValue) // well, probably