qemu: Do not include file if not exists

Script configure checks for if_alg.h and check failed but
if_alg.h still included.

Upstream-Status: Submitted [https://lists.gnu.org/archive/html/qemu-devel/2020-03/msg07188.html]
Signed-off-by: Oleksiy Obitotskyy <[email protected]>

[update patch context]
Signed-off-by: Sakib Sajal <[email protected]>

Author: mobbitster

linux-user/syscall.c

@@ -118,7 +118,9 @@
 #include <linux/blkpg.h>
 #include <netpacket/packet.h>
 #include <linux/netlink.h>
+#if defined(CONFIG_AF_ALG)
 #include <linux/if_alg.h>
+#endif
 #include <linux/rtc.h>
 #include <sound/asound.h>
 #ifdef HAVE_BTRFS_H