Updated CMakeLists.txt for relocatable installs

Forcing CMAKE_INSTALL_LIBDIR and CMAKE_INSTALL_INCLUDEDIR to be absolute is unnecessary and results in absolute paths in the installation. This prevents relocatable prefix installations.

CMakeLists.txt

@@ -143,13 +143,6 @@ endif()
 
 install(FILES tinyxml2.h DESTINATION ${CMAKE_INSTALL_INCLUDEDIR})
 
-foreach(p LIB INCLUDE)
-	set(var CMAKE_INSTALL_${p}DIR)
-	if(NOT IS_ABSOLUTE "${${var}}")
-		set(${var} "${CMAKE_INSTALL_PREFIX}/${${var}}")
-	endif()
-endforeach()
-
 configure_file(tinyxml2.pc.in tinyxml2.pc @ONLY)
 install(FILES ${CMAKE_CURRENT_BINARY_DIR}/tinyxml2.pc DESTINATION ${CMAKE_INSTALL_LIBDIR}/pkgconfig)