I believe we no longer require LLVM_HAS_INITIALIZER_LISTS; it's supported in...

I believe we no longer require LLVM_HAS_INITIALIZER_LISTS; it's supported in MSVC 2013 and GCC. Added a trivial test to ensure the ArrayRef initializer list constructor is called and behaves as expected.

If any of the bots complain (perhaps due to an antiquated version of an STL implementation), I will revert.

llvm-svn: 229502