D65562 moves LangStandard.h from clang/Frontend to clang/Basic. This patch
adjusts the single file in lldb that uses it to match.
Tested on x86_64-pc-linux-gnu. Ok for trunk?
One thing I'm unsure about is the scenario of building lldb with an existing (pre-Langstandard.h move)
clang: is this supposed to work in the general case and if so, how to deal with the two
possible paths for the header? I couldn't find an example of this in lldb.