linux-user: Fix compilation for "old" linux versions

Debian Lenny and other installations with older linux versions
failed to compile linux-user because some CLONE_xxx macros are
undefined.

Signed-off-by: Stefan Weil <weil@mail.berlios.de>
Signed-off-by: Riku Voipio <riku.voipio@iki.fi>

linux-user/strace.c

@@ -477,12 +477,24 @@ UNUSED static struct flags clone_flags[] = {
     FLAG_GENERIC(CLONE_DETACHED),
     FLAG_GENERIC(CLONE_UNTRACED),
     FLAG_GENERIC(CLONE_CHILD_SETTID),
+#if defined(CLONE_NEWUTS)
     FLAG_GENERIC(CLONE_NEWUTS),
+#endif
+#if defined(CLONE_NEWIPC)
     FLAG_GENERIC(CLONE_NEWIPC),
+#endif
+#if defined(CLONE_NEWUSER)
     FLAG_GENERIC(CLONE_NEWUSER),
+#endif
+#if defined(CLONE_NEWPID)
     FLAG_GENERIC(CLONE_NEWPID),
+#endif
+#if defined(CLONE_NEWNET)
     FLAG_GENERIC(CLONE_NEWNET),
+#endif
+#if defined(CLONE_IO)
     FLAG_GENERIC(CLONE_IO),
+#endif
     FLAG_END,
 };