configure_package_config_file: force absolute paths for usr-move

The configure_package_config()_file() macro will now use
absolute paths for the PATH_VARS if the Config.cmake file
will be installed into /lib(64) or /usr/lib(64), since due to
the usr-move filesystem changes Config.cmake files installed
there may be found via two paths (once per symlink via
/lib(64) and once via /usr/lib ), and in this case
relative paths break.

Alex

Modules/CMakePackageConfigHelpers.cmake

@@ -173,18 +173,34 @@ function(CONFIGURE_PACKAGE_CONFIG_FILE _inputFile _outputFile)
   else()
     set(absInstallDir "${CMAKE_INSTALL_PREFIX}/${CCF_INSTALL_DESTINATION}")
   endif()
+
+  # with the /usr-move, /lib(64) is a symlink to /usr/lib on Fedora, ArchLinux, Mageira and others.
+  # If we are installed to such a location, force using absolute paths.
+  set(forceAbsolutePaths FALSE)
+  if("${absInstallDir}" MATCHES "^(/usr)?/lib(64)?/.+")
+    set(forceAbsolutePaths TRUE)
+  endif()
+
   file(RELATIVE_PATH PACKAGE_RELATIVE_PATH "${absInstallDir}" "${CMAKE_INSTALL_PREFIX}" )
 
   foreach(var ${CCF_PATH_VARS})
     if(NOT DEFINED ${var})
       message(FATAL_ERROR "Variable ${var} does not exist")
     else()
+      if(forceAbsolutePaths)
+        if(IS_ABSOLUTE "${${var}}")
+          set(PACKAGE_${var} "${${var}}")
+        else()
+          set(PACKAGE_${var} "${CMAKE_INSTALL_PREFIX}/${${var}}")
+        endif()
+      else()
       if(IS_ABSOLUTE "${${var}}")
         string(REPLACE "${CMAKE_INSTALL_PREFIX}" "\${PACKAGE_PREFIX_DIR}"
                         PACKAGE_${var} "${${var}}")
       else()
         set(PACKAGE_${var} "\${PACKAGE_PREFIX_DIR}/${${var}}")
       endif()
+      endif()
     endif()
   endforeach()