Consolidate Linux recvfrom implementation

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

  1. Define __ASSUME_RECVFROM_SYSCALL by default
  2. Undef it for  architectures that do not support __NR_recvfrom.

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/alpha/syscalls.list: Remove recvfrom 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/sparc/sparc64/syscalls.list: Likewise.
	* sysdeps/unix/sysv/linux/x86_64/syscalls.list: Likewise.
	* sysdeps/unix/sysv/linux/mips/syscalls.list: Likewise.
	* sysdeps/unix/sysv/linux/i386/kernel-features.h
	* sysdeps/unix/sysv/linux/kernel-features.h
	(__ASSUME_RECVFROM_SYSCALL): Define by default.
	(__ASSUME_RECVFROM_SYSCALL): Undef it if kernel does not support
	__NR_recvfrom.
	* sysdeps/unix/sysv/linux/m68k/kernel-features.h
	(__ASSUME_RECVFROM_SYSCALL): Likewise.
	* sysdeps/unix/sysv/linux/s390/kernel-features.h
	(__ASSUME_RECVFROM_SYSCALL): Likewise.
	* sysdeps/unix/sysv/linux/microblaze/kernel-features.h
	(__ASSUME_RECVFROM_SYSCALL): Remove definition.
	* sysdeps/unix/sysv/linux/powerpc/kernel-features.h
	(__ASSUME_RECVFROM_SYSCALL): Likewise.
	* sysdeps/unix/sysv/linux/sh/kernel-features.h
	(__ASSUME_RECVFROM_SYSCALL): Likewise.
	* sysdeps/unix/sysv/linux/sparc/kernel-features.h
	(__ASSUME_RECVFROM_SYSCALL): Likewise.
	* sysdeps/unix/sysv/linux/recvfrom.c: Simplify includes.

sysdeps/unix/sysv/linux/sparc/kernel-features.h

@@ -41,6 +41,7 @@
 #if !defined __arch64__
 # undef __ASSUME_ACCEPT_SYSCALL
 # undef __ASSUME_CONNECT_SYSCALL
+# undef __ASSUME_RECVFROM_SYSCALL
 #endif
 
 /* sparc only supports ipc syscall.  */