Merge branch 'objc++' into maint

Merge branch 'objc++' into maint

* objc++:
  objc, objc++: test support for compilation flags
  objc, objc++: add stress test
  objc, objc++: test automatic dependency tracking
  objc: reorganize basic tests
  objc++, objc: add first semantic tests
  objc++: add first basic test
  news: announce initial support for Objective C++
  objc++: test support for '.mm' suffix in _SOURCES entries
  objc++: add documentation
  objc++: initial support for Objective C++

Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>