Consolidate Linux send implementation

Consolidate Linux send implementation

This patch consolidates the send Linux syscall implementation on
sysdeps/unix/sysv/linux/send{to}.c.  The changes are:

  1. Remove send from auto-generation syscalls.list on the architecture
     that uses __NR_send.
  2. Define __NR_send for architectures that supports it. It was done instead
     of defining in default kernel-features.h because current Linux practice
     for new ports are to implement only __NR_sendto [1] and it will
     require adding new kernel-features for ports that do not require it
     (aarch64 for instance).
  3. Remove __ASSUME_SENDTO_FOR_SEND_SYSCALL and decide to use
     __NR_sendto for send generation based on __ASSUME_SENDTO_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/sysdep.h (HAVE_INTERNAL_SEND_SYMBOL):
	Define.
	* sysdeps/unix/sysv/linux/aarch64/sysdep.h
	(HAVE_INTERNAL_SEND_SYMBOL): Undefine.
	* sysdeps/unix/sysv/linux/nios2/sysdep.h
	(HAVE_INTERNAL_SEND_SYMBOL): Likewise.
	* sysdeps/unix/sysv/linux/tile/sysdep.h
	(HAVE_INTERNAL_SEND_SYMBOL): Likewise.
	* sysdeps/unix/sysv/linux/alpha/kernel-features.h
	(__ASSUME_RECV_SYSCALL): Define.
	* sysdeps/unix/sysv/linux/arm/kernel-features.h
	(__ASSUME_RECV_SYSCALL): Likewise.
	* sysdeps/unix/sysv/linux/hppa/kernel-features.h
	(__ASSUME_RECV_SYSCALL): Likewise.
	* sysdeps/unix/sysv/linux/ia64/kernel-features.h
	(__ASSUME_RECV_SYSCALL): Likewise.
	* sysdeps/unix/sysv/linux/mips/kernel-features.h
	(__ASSUME_RECV_SYSCALL): Likewise.
	* sysdeps/unix/sysv/linux/i386/kernel-features.h
	(__ASSUME_SENDTO_FOR_SEND_SYSCALL): Remove define.
	* sysdeps/unix/sysv/linux/m68k/kernel-features.h
	(__ASSUME_SENDTO_FOR_SEND_SYSCALL): Likewise.
	* sysdeps/unix/sysv/linux/s390/kernel-features.h
	(__ASSUME_SENDTO_FOR_SEND_SYSCALL): Likewise.
	* sysdeps/unix/sysv/linux/alpha/syscalls.list: Remove send from
	auto-generation list.
	* sysdeps/unix/sysv/linux/arm/syscalls.list: Likewise.
	* sysdeps/unix/sysv/linux/hppa/syscalls.list: Likewise.
	* sysdeps/unix/sysv/linux/ia64/syscalls.list: Likewike.
	* sysdeps/unix/sysv/linux/mips/syscalls.list: Likewise.
	* sysdeps/unix/sysv/linux/sparc/sparc64/syscalls.list: Likewise.
	* sysdeps/unix/sysv/linux/send.c: Simplify includes.
	(__ASSUME_SENDTO_FOR_SEND_SYSCALL): Replace by
	__ASSUME_SENDTO_SYSCALL.
	* sysdeps/unix/sysv/linux/x86_64/send.c: Remove file.
	* sysdeps/unix/sysv/linux/mips/mips64/send.c: Likewise.
	* sysdeps/unix/sysv/linux/generic/send.c: Likewise.