Import libcxxrt 47661d00cd4d6cd728ae31b0bb29a49a6c06272a

The repository moved to https://github.com/libcxxrt/libcxxrt in the mean
time, but keep it on the same branch as before. This primarily bring

Import libcxxrt 47661d00cd4d6cd728ae31b0bb29a49a6c06272a

The repository moved to https://github.com/libcxxrt/libcxxrt in the mean
time, but keep it on the same branch as before. This primarily brings
C++14 support.

show more ...

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/.