unittests/ADT/ArrayRefTest.cpp: Suppress r243995 on g++-4.8 for now to unbreak bots.

For example of mingw-w64-g++-4.8.1,

  llvm/unittests/ADT/ArrayRefTest.cpp: In member function 'virtual void {anonymous}::ArrayRefTest_AllocatorCopy_Test::TestBody()':
  llvm/unittests/ADT/ArrayRefTest.cpp:56:40: internal compiler error: in count_type_elements, at expr.c:5523
     } Array3Src[] = {{"hello"}, {"world"}};
                                          ^
  Please submit a full bug report,
  with preprocessed source if appropriate.

llvm-svn: 244017