Add support for option -I in the new Flang driver.
This will allow for included headers and module files in other directories, as the default search path is currently the working folder.
The behaviour of this is consistent with the current f18 driver, where the current folder (i.e. ".") has the highest priority followed by the order of '-I's taking priority from first to last.
Summary of changes:
- Add SearchDirectoriesFromDashI to PreprocessorOptions, to be forwarded into the parser's searchDirectories
- Add header files and non-functional module files to be used in regression tests. The module files are just text files and are used to demonstrated that paths specified with -I are taken into account when searching for .mod files.
Depends on: D93401