[libcxx] Reexport std::bad_array_length symbols from libc++abi on OS X.

On OS X libc++ needs to reexport libc++abi's symbols in order for them to be provided. We explicitly list the symbols to reexport it libcxx/lib/libc++abi2.exp. This patch adds the symbols required by std::bad_array_length which have been missing for some time.

However there is a problem. std::bad_array_length was add to libc++abi in September of 2013 by commit r190479, about a year after everything else. Therefore I think older OS X version  have libc++abi versions without std::bad_array_length. On those systems
libc++ won't build with this change because we will try and export undefined symbols.

The workaround I would write to support older systems depends on the amount of people who would need it.   If only a small number of developers are affected it might be sufficient to provide a CMake switch like `LIBCPP_LIBCPPABI_HAS_BAD_ARRAY_LENGTH` which is
ON by default and can be disabled by those who need it. Otherwise I think we should try to automatically detect if the symbols are present in `/usr/lib/libc++abi.dylib` and configure accordingly. I would prefer the first solution because writing CMake sucks.

Reviewers: mclow.lists, aprantl

Subscribers: aprantl, cfe-commits

Differential Revision: http://reviews.llvm.org/D13445

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@249339 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed