Fix Linux sh4 pread/pwrite argument passing

Fix Linux sh4 pread/pwrite argument passing

Although conceptually correct for p{read,write}{64} offset argument passing,
sh4 implementation does not generate the correct expected code.  The
__ALIGNMENT_ARG redefinition is incorrect for two reasons: 1. the
kernel-features.h header is included multiple times (since it contains no
guards) and 2. the value it redefines is also incorrect (should be '0, '
instead of empty definition).

This patch fixes it by adding another macro, SYSCALL_LL_PRW{64}, meant to be
used to pass the offset argument on p{read,write}64.  It is basically the
already define SYSCALL_LL{64} plus __ALIGNMENT_ARG unless __ASSUME_PRW_DUMMY_ARG
is define.  In this case an empty dummy argument is used regardless how
__ALIGNMENT_ARG is defined (sh4 case).

Checked on x86_64, i686, aarch64, armhf, and powerpc64le (basically a sanity
check).  Also, John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de> and
James Clarke <jrtc27@jrtc27.com> help me check on a debian sh4 bootstrap using
2.24 plus this patch to verify it also corrected fixed the regression issue.

I also verified the generated object for a 2.24 build and master with this
patch for sh4 and both look identical.

	* sysdeps/unix/sysv/linux/pread.c (__libc_pread): Use SYSCALL_LL_PRW.
	* sysdeps/unix/sysv/linux/pwrite.c (__libc_pwrite): Likewise.
	* sysdeps/unix/sysv/linux/pread64.c (__libc_pread64): Use
	SYSCALL_LL64_PRW.
	* sysdeps/unix/sysv/linux/pwrite64.c (__libc_pwrite64): Likewise.
	* sysdeps/unix/sysv/linux/sh/kernel-features.h: Define
	__ASSUME_PRW_DUMMY_ARG.
	* sysdeps/unix/sysv/linux/sh/pread.c: Remove file.
	* sysdeps/unix/sysv/linux/sh/pread64.c: Likewise.
	* sysdeps/unix/sysv/linux/sh/pwrite.c: Likewise.
	* sysdeps/unix/sysv/linux/sh/pwrite64.c: Likewise.
	* sysdeps/unix/sysv/linux/sysdep.h: Define SYSCALL_LL_PRW and
	SYSCALL_LL_PRW64 based on __ASSUME_PRW_DUMMY_ARG.