The implementation is in AnalysisDeclContext.cpp and the class is called
AnalysisDeclContext.

Making those match up has numerous benefits, including:

 - Easier jump from header to/from implementation.
 - Easily identify filename from class.

Differential Revision: https://reviews.llvm.org/D37500

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@312671 91177308-0d34-0410-b5e6-96231b3b80d8