write a line marker right before adding included file

Enclosing the original #include directive inside #if 0 adds lines,
so warning/errors messages would have the line number off in
"In file included from <file>:<line>:", so add line marker to fix this.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@207756 91177308-0d34-0410-b5e6-96231b3b80d8