* toplev.c (documented_lang_options): Recognize -include,
        -imacros, -iwithprefix, -iwithprefixbefore.
        * cpplib.c (cpp_start_read): Process -imacros and -include
        switches at the same time and in command-line order, after
        initializing the dependency-output code.  Emit properly nested
        #line directives for them.  Emit a #line for the main file
        before processing these switches, and don't do it again
        afterward.

From-SVN: r22689