tools/x86: don't rebuild cpuid-autogen.h every time

tools/x86: don't rebuild cpuid-autogen.h every time

The first thing the "xen-dir" rule does is delete the entire xen/
subtree. Obviously this includes deleting xen/lib/x86/*autogen.h. As a
result there's no original version for $(move-if-changed ...) to compare
against, and hence the file and all its consumers would get rebuilt
every time. Instead only find and delete all the symlinks.

Fixes: eddf9559c977 ("libx86: generate cpuid-autogen.h in the libx86 include dir")
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Ian Jackson <iwj@xenproject.org>
Release-Acked-by: Ian Jackson <iwj@xenproject.org>