You probably want to replace use link_directorieswith find_libraryand target_link_libraries.
link_directories , - , . , :
, . , find_package() find_library(), . target_link_libraries(). CMake , .
Xerces, , , libxerces-c.a, - :
find_library(XercesLibrary NAMES xerces-c PATHS /usr/local/lib)
if(NOT XercesLibrary)
message(FATAL_ERROR "Failed to find the Xerces library.")
endif()
...
target_link_libraries(MyExe ${XercesLibrary})
, find_library ; PATHS, /usr/local/lib; (, Windows?) .. , NAME (, CMake - . CMAKE_FIND_LIBRARY_PREFIXES CMAKE_FIND_LIBRARY_SUFFIXES).
, , . (, XERCES_LIB_DIR), Xerces, PATHS find_library.