-include FILE'
Process FILE as if '#include "file"' appeared as the first line of
the primary source file. However, the first directory searched for
FILE is the preprocessor's working directory _instead of_ the
directory containing the main source file. If not found there, it
is searched for in the remainder of the '#include "..."' search
chain as normal.
If multiple '-include' options are given, the files are included in
the order they appear on the command line.