Move SanitizerKind class to a separate header. NFC.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@221645 91177308-0d34-0410-b5e6-96231b3b80d8
Move CodeGenOptions constructor out-of-line and add missing headers. NFC.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@221646 91177308-0d34-0410-b5e6-96231b3b80d8