* collect2.c (find_a_file): Use HAVE_DOS_BASED_FILE_SYSTEM in place

        of the DIR_SEPARATOR test.
        Consider any file starting with a drivename to be absolute.
        If the absolute filename test fails and EXECUTABLE_SUFFIX is
        defined, append EXECUTABLE_SUFFIX to the file and try again.
        * cppinit.c (base_name): Use HAVE_DOS_BASED_FILE_SYSTEM
        in place of __MSDOS__ and _WIN32.
        * cppfiles.c (simplify_pathname): Likewise.
        * gcc.c (IS_DIR_SEPARATOR): Define new macro. Returns true if a
        character is a directory separator.
        (find_a_file): Use it.
        (convert_filename): Likewise.
        (process_command): Likewise.
        (do_spec_1): Likewise.
        (is_directory): Likewise.
        (main): Likewise.
        * prefix.c (IS_DIR_SEPARATOR): Define. Tests whether a character is
        a directory separator.
        (translate_name): Use it.
        (update_path): Change DIR_SEPARATOR_2 to DIR_SEPARATOR. Fix
        warning in block where '/' is changed to DIR_SEPARATOR.
        * i386/xm-djgpp.h (DIR_SEPARATOR): Set to '/'.
        (DIR_SEPARATOR_2): New macro. Set to '\'.
        (HAVE_DOS_BASED_FILESYS): Define.
        * i386/xm-mingw32.h: Updated copyright. Set
        DIR_SEPARATOR_2 to '/'. Define HAVE_DOS_BASED_FILE_SYSTEM.
        * i386/xm-os2.h: Likewise.
        * winnt/xm-winnt.h: Likewise.
        * i386/xm-dos.h: Likewise.  Add copyright.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@26328 138bc75d-0d04-0410-961f-82ee72b054a4