fix build with CONFIG_HYPFS_CONFIG enabled
Commit
58263ed7713e ("xen: add /buildinfo/config entry to hypervisor
filesystem") added a dependency to .config, but the hypervisor's build
config could be have another name via setting KCONFIG_CONFIG.
Fix that by using $(KCONFIG_CONFIG) instead. Additionally reference
the config file via $(XEN_ROOT) instead of a relative path.
Reported-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>