Consolidate Linux accept implementation

This patch consolidates the accept Linux syscall implementation on
sysdeps/unix/sysv/linux/accept.c.  The changes are:

  1. Remove accept from auto-generation syscalls.list on the architecture
     that uses __NR_accept.
  2. Define __NR_accept as default (__ASSUME_ACCEPT_SYSCALL) and undef for
     architectures that do not support it.
  3. Remove __ASSUME_ACCEPT4_FOR_ACCEPT_SYSCALL and decide to use
     __NR_accept4 for accept generation based on __ASSUME_ACCEPT4_SYSCALL.

Checked on i686-linux-gnu, x86_64-linux-gnu, x86_64-linux-gnux32,
aarch64-linux-gnu, arm-linux-gnueabihf, and powerpc64le-linux-gnu.

	* sysdeps/unix/sysv/linux/accept.c (__libc_accept): Replace
	__ASSUME_ACCEPT4_FOR_ACCEPT_SYSCALL by __ASSUME_ACCEPT4_SYSCALL.
	* sysdeps/unix/sysv/linux/alpha/syscalls.list: Remove accept from
	auto-generation list.
	* sysdeps/unix/sysv/linux/arm/syscalls.list: Likewise.
	* sysdeps/unix/sysv/linux/generic/syscalls.list: Likewise.
	* sysdeps/unix/sysv/linux/hppa/syscalls.list: Likewise.
	* sysdeps/unix/sysv/linux/ia64/syscalls.list: Likewise.
	* sysdeps/unix/sysv/linux/mips/syscalls.list: Likewise.
	* sysdeps/unix/sysv/linux/sparc/sparc64/syscalls.list: Likewise.
	* sysdeps/unix/sysv/linux/x86_64/syscalls.list: Likewise.
	* sysdeps/unix/sysv/linux/i386/kernel-features.h
	(__ASSUME_ACCEPT4_FOR_ACCEPT_SYSCALL): Remove define.
	(__ASSUME_ACCEPT_SYSCALL): Undefine.
	* sysdeps/unix/sysv/linux/kernel-features.h
	(__ASSUME_ACCEPT_SYSCALL): New define.
	* sysdeps/unix/sysv/linux/m68k/kernel-features.h
	(__ASSUME_ACCEPT4_FOR_ACCEPT_SYSCALL): Remove define.
	(__ASSUME_ACCEPT_SYSCALL): Define wheter kernel version supports.
	* sysdeps/unix/sysv/linux/microblaze/kernel-features.h
	(__ASSUME_ACCEPT_SYSCALL): Define.
	* sysdeps/unix/sysv/linux/powerpc/kernel-features.h
	(__ASSUME_ACCEPT_SYSCALL): Undefine.
	* sysdeps/unix/sysv/linux/s390/kernel-features.h
	(__ASSUME_ACCEPT4_FOR_ACCEPT_SYSCALL): Remove define.
	(__ASSUME_ACCEPT_SYSCALL): Undefine.
	* sysdeps/unix/sysv/linux/sh/kernel-features.h
	(__ASSUME_ACCEPT_SYSCALL): Undefine.
	* sysdeps/unix/sysv/linux/sparc/kernel-features.h
	(__ASSUME_ACCEPT_SYSCALL): Undefine for 32 bits.