Revert r152745 as it's breaking the internal buildbots.

Abbreviated commit message:
Provide -Wnull-conversion separately from -Wconversion.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@152765 91177308-0d34-0410-b5e6-96231b3b80d8
6 files changed