linux-user/syscall.c: add target-to-host mapping for epoll_create1()

linux-user/syscall.c: add target-to-host mapping for epoll_create1()

Noticed by Barnabás Virágh as a python-3.7 failue on qemu-alpha.

The bug shows up on alpha as it's one of the targets where
EPOLL_CLOEXEC differs from other targets:
    sysdeps/unix/sysv/linux/alpha/bits/epoll.h: EPOLL_CLOEXEC  = 01000000
    sysdeps/unix/sysv/linux/bits/epoll.h:        EPOLL_CLOEXEC = 02000000

Bug: https://bugs.gentoo.org/717548
Reported-by: Barnabás Virágh
Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>
CC: Riku Voipio <riku.voipio@iki.fi>
CC: Laurent Vivier <laurent@vivier.eu>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <20200415220508.5044-1-slyfox@gentoo.org>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>