shlwapi/tests: Fix compilation on systems that don't support nameless unions.

dlls/shlwapi/tests/istream.c

@@ -675,7 +675,7 @@ static void test_SHCreateStreamOnFileEx_CopyTo(void)
     ok(SUCCEEDED(ret), "SHCreateStreamOnFileEx failed with ret=0x%08x\n", ret);
 
     written.QuadPart = 0;
-    ret = IStream_Write(src, srcContents, sizeof(srcContents), &written.LowPart);
+    ret = IStream_Write(src, srcContents, sizeof(srcContents), &U(written).LowPart);
     ok(SUCCEEDED(ret), "ISequentialStream_Write failed with ret=0x%08x\n", ret);
 
     distance.QuadPart = 0;
@@ -691,8 +691,8 @@ static void test_SHCreateStreamOnFileEx_CopyTo(void)
     ret = IStream_CopyTo(src, dst, count, &read, &written);
     ok(SUCCEEDED(ret), "CopyTo failed with ret=0x%08x\n", ret);
 
-    ok(read.QuadPart == 1, "read does not match size: %d != 1\n", read.LowPart);
-    ok(written.QuadPart == 1, "written does not match size: %d != 1\n", written.LowPart);
+    ok(read.QuadPart == 1, "read does not match size: %d != 1\n", U(read).LowPart);
+    ok(written.QuadPart == 1, "written does not match size: %d != 1\n", U(written).LowPart);
 
     IStream_Release(dst);
     IStream_Release(src);