Add code coverage mapping data, reader, and writer.

This patch implements the data structures, the reader and
the writers for the new code coverage mapping system. 
The new code coverage mapping system uses the instrumentation
based profiling to provide code coverage analysis.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@213910 91177308-0d34-0410-b5e6-96231b3b80d8