* ldd.cc: Rework to detect missing DLLs.

* ldd.cc: Rework to detect missing DLLs.
(start_process): Change to expect windows filename as input.
(tocyg): New function - convert cygwin fn to windows fn.
(print_dlls_and_kill_inferior): Accept extra argument denoting whether to open
input and look for nonexistent DLLs.  Use tocyg to convert filename and pass it
to start_process.
(report): Flag when an DLL-not-found exception occurs and pass this information
to print_dlls_and_kill_inferior.
(filelist): New structure.
(saw_file): New function.
(dump_import_directory): Ditto.
(map_file): Ditto.
(skip_dos_stub): Ditto.
(get_directory_index): Ditto.
(process_file): Ditto.