[CMake] Use empty endif() and else() statements in generated scripts.

We follow the advice of upstream and use only empty endif() and
else() statements in new code. The removal of the optional argument
is only in generated scripts.

cmake/modules/DuneDoxygen.cmake

@@ -79,7 +79,7 @@ MACRO (add_doxygen_target)
       foreach(_file \${doxygenfiles})
          get_filename_component(_basename \${_file} NAME)
          LIST(APPEND CMAKE_INSTALL_MANIFEST_FILES ${CMAKE_INSTALL_FULL_DOCDIR}/doxygen/\${_basename})
-       endforeach(_file in \${doxygenfiles})
+       endforeach()
        file(INSTALL \${doxygenfiles} DESTINATION ${CMAKE_INSTALL_FULL_DOCDIR}/doxygen)
        message(STATUS \"Installed doxygen into ${CMAKE_INSTALL_FULL_DOCDIR}/doxygen\")")
 

cmake/modules/DuneMacros.cmake

@@ -781,12 +781,12 @@ ${DUNE_CUSTOM_PKG_CONFIG_SECTION}
 if(${ProjectName}_LIBRARIES)
   get_filename_component(_dir \"\${CMAKE_CURRENT_LIST_FILE}\" PATH)
   include(\"\${_dir}/${ProjectName}-targets.cmake\")
-endif(${ProjectName}_LIBRARIES)
-endif(NOT ${ProjectName}_FOUND)")
+endif()
+endif()")
       set(CONFIG_SOURCE_FILE ${PROJECT_BINARY_DIR}/CMakeFiles/${ProjectName}-config.cmake.in)
-  else(NOT EXISTS ${PROJECT_SOURCE_DIR}/cmake/pkg/${ProjectName}-config.cmake.in)
+  else()
     set(CONFIG_SOURCE_FILE ${PROJECT_SOURCE_DIR}/cmake/pkg/${ProjectName}-config.cmake.in)
-  endif(NOT EXISTS ${PROJECT_SOURCE_DIR}/cmake/pkg/${ProjectName}-config.cmake.in)
+  endif()
   get_property(DUNE_MODULE_LIBRARIES GLOBAL PROPERTY DUNE_MODULE_LIBRARIES)
 
   # compute under which libdir the package configuration files are to be installed.
@@ -797,9 +797,9 @@ endif(NOT ${ProjectName}_FOUND)")
   get_property(DUNE_MODULE_LIBRARIES GLOBAL PROPERTY DUNE_MODULE_LIBRARIES)
   if(DUNE_MODULE_LIBRARIES)
     set(DUNE_INSTALL_LIBDIR ${CMAKE_INSTALL_LIBDIR})
-  else(DUNE_MODULE_LIBRARIES)
+  else()
     set(DUNE_INSTALL_LIBDIR ${DUNE_INSTALL_NONOBJECTLIBDIR})
-  endif(DUNE_MODULE_LIBRARIES)
+  endif()
 
   # Set the location of the doc file source. Needed by custom package configuration
   # file section of dune-grid.