Previous workaround to the xen upgrade race condition actually caused
xen to be uninstalled on most systems, breaking the template. This is
thus another approach at fixing the race condition by linking against
non-versionned xen libraries. Thus, a minor version upgrade of xen will
not cause libxenvchan.so to lose xen libraries.
The linking process is changed by adding a step before linking where ld
is linked against libraries where DT_SONAME has been patched with
patchelf. This is not an elegant solution, but it does work. Ideally, we
would find a way for seamless upgrading of xen while the proxy is up.
