cygwin: include sys/types.h in sys/xattr.h

Using libattr's <xattr/xattr.h> requires consumers to explicitly include
<sys/types.h> first, but glibc's header in sys/ already contains the include.

Signed-off-by: Yaakov Selkowitz <yselkowi@redhat.com>

winsup/cygwin/include/sys/xattr.h

@@ -13,6 +13,7 @@ details. */
 #ifndef _SYS_XATTR_H
 #define _SYS_XATTR_H
 
+#include <sys/types.h>
 #include <attr/xattr.h>
 
 #endif /* _SYS_XATTR_H */