Consolidate preadv/preadv64 implementation

This patch consolidates all the preadv{64} implementation for Linux
in only one (sysdeps/unix/sysv/linux/preadv{64}.c).  It also removes the
syscall from the auto-generation using assembly macros.

It was based on previous pread/pread64 consolidation patch.  The new macro
SYSCALL_LL{64} is used to handle the offset argument and alias is created
for __ASSUME_OFF_DIFF_OFF64 in case of pread64.

Checked on x86_64, i386, aarch64, and powerpc64le.

	* misc/Makefile (CFLAGS-preadv.c): New variable: add cancellation
	required flags.
	(CFLAGS-preadv64.c): Likewise.
	* sysdeps/unix/sysv/linux/generic/wordsize-32/preadv.c: Remove file.
	* sysdeps/unix/sysv/linux/generic/wordsize-32/preadv64.c: Likewise.
	* sysdeps/unix/sysv/linux/mips/mips64/n64/preadv64.c: Likewise.
	* sysdeps/unix/sysv/linux/wordsize-64/preadv.c: Likewise.
	* sysdeps/unix/sysv/linux/wordsize-64/preadv64.: Likwise.
	* sysdeps/unix/sysv/linux/x86_64/x32/syscalls.list (preadv): Remove
	syscall from auto-generation.
	* sysdeps/unix/sysv/linux/preadv.c: Rewrite implementation.
	[WORDSIZE == 64] (preadv64): Remove macro.
	[!PREADV] (PREADV): Likewise.
	[!PREADV] (PREADV_REPLACEMENT): Likewise.
	[!PREADV] (PREAD): Likewise.
	[!PREADV] (OFF_T): Likewise.
	[!__ASSUME_PREADV] (PREADV_REPLACEMENT): Likewise.
	(LO_HI_LONG): Remove macro.
	[__WORDSIZE != 64 || __ASSUME_OFF_DIFF_OFF64] (preadv): Add function.
	* sysdeps/unix/sysv/linux/preadv64.c: Rewrite implementation.
	(PREADV): Remove macro.
	(PREADV_REPLACEMENTE): Likewise.
	(PREAD): Likewise.
	(OFF_T): Likewise.
	(preadv64): New function.
	* nptl/tst-cancel4.c (tf_preadv): Add test.

sysdeps/unix/sysv/linux/mips/mips64/n64/preadv64.c

@@ -1 +0,0 @@
-/* Empty since the preadv syscall is equivalent.  */