libc: rename TRUNCATE64_HAS_4_ARGS to SYSCALL_ALIGN_64BIT

The reason truncate64 takes 4 args on some arches is that their ABI
requires 64bit values to be aligned on register pair boundaries.
Since this alignment affects more than just truncate64, rename the
define to properly document its purpose.  This also allows us to
expand it to the other impacted syscalls (which will be done in a
follow up commit).

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
(cherry picked from commit e8cc14e59ed3f66b84eedcc6ece65d40540edf47)
linux: pread: fix __NR___syscall_pread define

We set up __NR_pread to be the right value, but the code then uses
__NR_pread64 all the time.  Fix it to use __NR_pread as we intended.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
linux: pread/pwrite: fix 64bit handling

This is a fix similar to 458076d59ef9849f79d27e21b6094b0b3a85fbb4.
But master has been rewritten heavily, so do a minor backport.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>