add a tool to generate symbol remapping files.
Summary:
The new tool llvm-cxxmap builds a symbol mapping table from a file containing
a description of partial equivalences to apply to mangled names and files
containing old and new symbol tables.
Reviewers: davidxl
Subscribers: mgorny, llvm-commits
Differential Revision: https://reviews.llvm.org/D51470
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@342168 91177308-0d34-0410-b5e6-96231b3b80d8
