add lib/CodeGen/CoverageMappingGen.cpp to CMake

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@214757 91177308-0d34-0410-b5e6-96231b3b80d8
Add CoverageMappingGen.cpp (introduced in r214752) to CMakeLists.txt

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@214758 91177308-0d34-0410-b5e6-96231b3b80d8
Revert r214757 (Same fix as r214758)

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@214759 91177308-0d34-0410-b5e6-96231b3b80d8