alpha: force old OSF1 syscalls for getegid, geteuid and getppid [BZ #24986]

On alpha, Linux kernel 5.1 added the standard getegid, geteuid and
getppid syscalls (commit ecf7e0a4ad15287). Up to now alpha was using
the corresponding OSF1 syscalls through:
 - sysdeps/unix/alpha/getegid.S
 - sysdeps/unix/alpha/geteuid.S
 - sysdeps/unix/alpha/getppid.S

When building against kernel headers >= 5.1, the glibc now use the new
syscalls through sysdeps/unix/sysv/linux/syscalls.list. When it is then
used with an older kernel, the corresponding 3 functions fail.

A quick fix is to move the OSF1 wrappers under the
sysdeps/unix/sysv/linux/alpha directory so they override the standard
linux ones. A better fix would be to try the new syscalls and fallback
to the old OSF1 in case the new ones fail. This can be implemented in
a later commit.

Changelog:
	[BZ #24986]
        * sysdeps/unix/alpha/getegid.S: Move to ...
	* sysdeps/unix/sysv/linux/alpha/getegid.S: ... here.
        * sysdeps/unix/alpha/geteuid.S: Move to ...
	* sysdeps/unix/sysv/linux/alpha/geteuid.S: ... here.
        * sysdeps/unix/alpha/getppid.S: Move to ...
	* sysdeps/unix/sysv/linux/alpha/getppid.S: ... here
(cherry picked from commit 1a656609)