Consolidate Linux read syscall

Consolidate Linux read syscall

This patch consolidates the read Linux syscall implementation on
sysdeps/unix/sysv/linux/read.c.  This leads to a different frame
pointer creation on some architectures:

  * It fixes BZ#21428 on aarch64, since now the returned address
    for the read syscall can be correctly found out by
    backtrace_symbols.

  * It makes tst-backtrace{5,6} fails on powerpc due an issue on
    its custom backtrace implementation.  It is fixed on subsequent
    patch from this set.

Checked on i686-linux-gnu, x86_64-linux-gnu, x86_64-linux-gnux32,
arch64-linux-gnu, arm-linux-gnueabihf, and powerpc64le-linux-gnu.

	[BZ #21428]
	* include/unistd.h (read): Add hidden proto.
	* io/Makefile (CFLAGS-read.c): New rule.
	* nptl/Makefile (CFLAGS-read.c): New rule.
	* sysdeps/unix/sysv/linux/read.c: New file.