Merge from Mainline

git-svn-id: https://svn.dealii.org/branches/branch_port_to_libcxx@30217 0785d39b-7218-0410-832d-ea1e28bc413d

diff --cc deal.II/cmake/macros/macro_enable_language_optional.cmake
index 885b960f8c47e52b43a83210f6d029ca3b19fe8b,885b960f8c47e52b43a83210f6d029ca3b19fe8b..fccb978ae428c08c9b4a1fe79ae2d41712476a1d
--- 1/deal.II/cmake/macros/macro_enable_language_optional.cmake
--- 2/deal.II/cmake/macros/macro_enable_language_optional.cmake
+++ b/deal.II/cmake/macros/macro_enable_language_optional.cmake
@@@ -32,10 -32,10 +32,10 @@@
  #
  
  MACRO(ENABLE_LANGUAGE_OPTIONAL _language)
--  #
--  # Run this check exactly once:
--  #
    IF(NOT ${_language}_CHECKED)
++    #
++    # Run this check exactly once:
++    #
      SET(${_language}_CHECKED TRUE CACHE INTERNAL "" FORCE)
  
      SET(_tmp ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeTmp/${_language}_test)
@@@ -58,9 -58,9 +58,17 @@@
        )
  
      IF("${_result}" STREQUAL "0")
++      SET(DEAL_II_${_language}_COMPILER_WORKS TRUE CACHE INTERNAL "" FORCE)
        ENABLE_LANGUAGE(${_language})
      ELSE()
        MESSAGE(STATUS "No working ${_language} compiler found, disabling ${_language}")
      ENDIF()
++  ELSE()
++    #
++    # Enable the language depending on the cached result from a former run:
++    #
++    IF(DEAL_II_${_language}_COMPILER_WORKS)
++      ENABLE_LANGUAGE(${_language})
++    ENDIF()
    ENDIF()
  ENDMACRO()