CLEANUP: drop support for USE_MY_ACCEPT4

The accept4() syscall has been present for a while now, there is no more
reason for maintaining our own arch-specific syscall implementation for
systems lacking it in libc but having it in the kernel.
diff --git a/Makefile b/Makefile
index 9596407..75ce791 100644
--- a/Makefile
+++ b/Makefile
@@ -39,7 +39,6 @@
 #   USE_LUA              : enable Lua support.
 #   USE_FUTEX            : enable use of futex on kernel 2.6. Automatic.
 #   USE_ACCEPT4          : enable use of accept4() on linux. Automatic.
-#   USE_MY_ACCEPT4       : use own implementation of accept4() if glibc < 2.10.
 #   USE_PRCTL            : enable use of prctl(). Automatic.
 #   USE_ZLIB             : enable zlib library support.
 #   USE_SLZ              : enable slz library instead of zlib (pick at most one).
@@ -290,7 +289,7 @@
            USE_STATIC_PCRE USE_STATIC_PCRE2 USE_TPROXY USE_LINUX_TPROXY       \
            USE_LINUX_SPLICE USE_LIBCRYPT USE_CRYPT_H                          \
            USE_GETADDRINFO USE_OPENSSL USE_LUA USE_FUTEX USE_ACCEPT4          \
-           USE_MY_ACCEPT4 USE_ZLIB USE_SLZ USE_CPU_AFFINITY USE_TFO USE_NS    \
+           USE_ZLIB USE_SLZ USE_CPU_AFFINITY USE_TFO USE_NS                   \
            USE_DL USE_RT USE_DEVICEATLAS USE_51DEGREES USE_WURFL USE_SYSTEMD  \
            USE_OBSOLETE_LINKER USE_PRCTL USE_THREAD_DUMP USE_EVPORTS
 
diff --git a/include/common/accept4.h b/include/common/accept4.h
deleted file mode 100644
index 19e231d..0000000
--- a/include/common/accept4.h
+++ /dev/null
@@ -1,69 +0,0 @@
-/*
- * include/common/accept4.h
- * Definition of the accept4 system call for older Linux libc.
- *
- * Copyright 2000-2012 Willy Tarreau <w@1wt.eu>
- *
- * This library is free software; you can redistribute it and/or
- * modify it under the terms of the GNU Lesser General Public
- * License as published by the Free Software Foundation, version 2.1
- * exclusively.
- *
- * This library is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
- * Lesser General Public License for more details.
- *
- * You should have received a copy of the GNU Lesser General Public
- * License along with this library; if not, write to the Free Software
- * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
- *
- */
-
-#ifndef _COMMON_ACCEPT4_H
-#define _COMMON_ACCEPT4_H
-
-#if defined (__linux__) && defined(USE_ACCEPT4)
-
-#include <sys/types.h>
-#include <sys/socket.h>
-#include <sys/syscall.h>
-#include <errno.h>
-#include <fcntl.h>
-#include <unistd.h>
-#include <common/syscall.h>
-
-/* On recent Linux kernels, the accept4() syscall may be used to avoid an fcntl()
- * call to set O_NONBLOCK on the resulting socket. It was introduced in Linux
- * 2.6.28 and is not present in older libcs.
- */
-#ifndef SOCK_NONBLOCK
-#define SOCK_NONBLOCK O_NONBLOCK
-#endif
-
-#if defined(USE_MY_ACCEPT4) || (!defined(SYS_ACCEPT4) && !defined(__NR_accept4))
-#if ACCEPT4_USE_SOCKETCALL
-static inline _syscall2(int, socketcall, int, call, unsigned long *, args);
-static int accept4(int sockfd, struct sockaddr *addr, socklen_t *addrlen, int flags)
-{
-	unsigned long args[4];
-
-	args[0] = (unsigned long)sockfd;
-	args[1] = (unsigned long)addr;
-	args[2] = (unsigned long)addrlen;
-	args[3] = (unsigned long)flags;
-	return socketcall(SYS_ACCEPT4, args);
-}
-#else
-static inline _syscall4(int, accept4, int, sockfd, struct sockaddr *, addr, socklen_t *, addrlen, int, flags);
-#endif /* ACCEPT4_USE_SOCKETCALL etc... */
-#endif /* USE_MY_ACCEPT4 */
-#endif /* __linux__ && USE_ACCEPT4 */
-#endif /* _COMMON_ACCEPT4_H */
-
-/*
- * Local variables:
- *  c-indent-level: 8
- *  c-basic-offset: 8
- * End:
- */
diff --git a/include/common/syscall.h b/include/common/syscall.h
index 9554d5a..b379a06 100644
--- a/include/common/syscall.h
+++ b/include/common/syscall.h
@@ -130,24 +130,6 @@
 #endif /* $arch */
 #endif /* __NR_splice */
 
-/* accept4() appeared in Linux 2.6.28, but it might not be in all libcs. Some
- * archs have it as a native syscall, other ones use the socketcall instead.
- */
-#ifndef __NR_accept4
-#if defined(__x86_64__)
-#define __NR_accept4            288
-#elif defined(__sparc__) || defined(__sparc64__)
-#define __NR_accept4            323
-#elif defined(__arm__) || defined(__thumb__)
-#define __NR_accept4            (__NR_SYSCALL_BASE+366)
-#else
-#define ACCEPT4_USE_SOCKETCALL    1
-#ifndef SYS_ACCEPT4
-#define SYS_ACCEPT4              18
-#endif /* SYS_ACCEPT4 */
-#endif /* $arch */
-#endif /* __NR_accept4 */
-
 #endif /* __linux__ */
 #endif /* _COMMON_SYSCALL_H */
 
diff --git a/src/listener.c b/src/listener.c
index 689cea8..e9a4bee 100644
--- a/src/listener.c
+++ b/src/listener.c
@@ -18,7 +18,6 @@
 #include <unistd.h>
 #include <fcntl.h>
 
-#include <common/accept4.h>
 #include <common/cfgparse.h>
 #include <common/config.h>
 #include <common/errors.h>