Fix warning about memmove re#definition.

diff --git a/include/wine/port.h b/include/wine/port.h
index 0cf8274..238c696 100644
--- a/include/wine/port.h
+++ b/include/wine/port.h
@@ -456,6 +456,7 @@
 #define interlocked_xchg_add    __WINE_NOT_PORTABLE(interlocked_xchg_add)
 #define lstat                   __WINE_NOT_PORTABLE(lstat)
 #define memcpy_unaligned        __WINE_NOT_PORTABLE(memcpy_unaligned)
+#undef memmove
 #define memmove                 __WINE_NOT_PORTABLE(memmove)
 #define pread                   __WINE_NOT_PORTABLE(pread)
 #define pwrite                  __WINE_NOT_PORTABLE(pwrite)