[Preprocessor] Support for '-dI' flag

Re-introduce r285411.

Implement the -dI as supported by GCC: Output ‘#include’ directives in addition
to the result of preprocessing.

This change aims to add this option, pass it through to the preprocessor via
the options class, and when inclusions occur we output some information (+ test
cases).

Patch by Steve O'Brien!

Differential Revision: https://reviews.llvm.org/D26089

llvm-svn: 287275