Merge 47661d00cd4d6cd728ae31b0bb29a49a6c06272a

Inline storage size in one place to avoid depending on DCE for removing
the USE_FORT=yes warning.

Import libcxxrt e64e93fe5bba67a6d52cbe5a97f8770c054bfa65

Implements __cxa_throw_bad_array_new_length, which is generated by gcc
4.9 and later. Also, some demangle support and fixes.

Import new snapshot of libcxxrt. Fixes demangling of anonymous
namespaces. Avoid use of old style (C) casts.

Import libcxxrt b2396b5945d7a2697c4762c3e52dc6f732b2eebd from
https://github.com/pathscale/libcxxrt/.