meson: accept relative symlinks in "meson introspect --installed" data

meson: accept relative symlinks in "meson introspect --installed" data

When installing shared libraries, as is the case for libvfio-user.so,
Meson will include relative symbolic links in the output of
"meson introspect --installed":

  {
    "libvfio-user.so": "/usr/local/lib64/libvfio-user.so",
    ...
  }

In the case of scripts/symlink-install-tree.py, this will
be a symbolic link to a symbolic link but, in any case, there is
no issue in creating it.

Cc: qemu-stable@nongnu.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
(cherry picked from commit f32eb0021a85efaca97f69b0e9201737562a8e4f)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>