pending "Treat dead Xalan-C as optional"
https://github.com/open-eid/cmake/pull/38

Index: cmake/modules/FindXmlSecurityC.cmake
--- cmake/modules/FindXmlSecurityC.cmake.orig
+++ cmake/modules/FindXmlSecurityC.cmake
@@ -22,7 +22,7 @@ select_library_configurations(XmlSecurityC)
 mark_as_advanced(XmlSecurityC_INCLUDE_DIR XmlSecurityC_LIBRARY_RELEASE XmlSecurityC_LIBRARY_DEBUG)
 
 include(FindPackageHandleStandardArgs)
-FIND_PACKAGE_HANDLE_STANDARD_ARGS(XmlSecurityC DEFAULT_MSG XmlSecurityC_LIBRARY XmlSecurityC_INCLUDE_DIR XalanC_FOUND XercesC_FOUND OPENSSL_FOUND)
+FIND_PACKAGE_HANDLE_STANDARD_ARGS(XmlSecurityC DEFAULT_MSG XmlSecurityC_LIBRARY XmlSecurityC_INCLUDE_DIR XercesC_FOUND OPENSSL_FOUND)
 
 if(XmlSecurityC_FOUND)
   set(XmlSecurityC_INCLUDE_DIRS ${XmlSecurityC_INCLUDE_DIR} ${XercesC_INCLUDE_DIR} ${OPENSSL_INCLUDE_DIR})