Allow cygwin_conv_path(3) and cygpath(1) to emit /proc/cygdrive prefixed path

* include/sys/cygwin.h (CCP_PROC_CYGDRIVE): New flag.
        * mount.cc (mount_info::cygdrive_posix_path): Take flag values rather
        than just a trailing_slash_p bool.  Emit /proc/cygdrive path if
        CCP_PROC_CYGDRIVE flag is given.
        (mount_info::conv_to_posix_path): Take flag values rather than just
        a keep_rel_p bool.  Rename _p variables.  Print flag value as hex in
        debug_printf.  Call cygdrive_posix_path with flag values.
        * mount.h (mount_info::cygdrive_posix_path): Accommodate above change
        in declaration.
        (mount_info::conv_to_posix_path): Ditto.
        * fhandler_process.cc (format_process_exename): Accommodate change to
        mount_info::conv_to_posix_path.
        * path.cc (cygwin_conv_path): Ditto.

        * cygpath.cc (absolute_flag): Initialize to CCP_RELATIVE to simplify
        expressions.
        (cygdrive_flag): New global flag.
        (long_options): Add --proc-cygdrive option.
        (options): Add -U option.
        (usage): Add description for -U option.
        (do_sysfolders): Or cygdrive_flag to cygwin_conv_path call.
        (do_pathconv): Simply or absolute_flag to conv_func.  Or
        cygdrive_flag to conv_func.
        (do_options): Initalize absolute_flag to CCP_RELATIVE.  Initialize new
        cygdrive_flag.  Set absolute_flag to CCP_ABSOLUTE on -a.  Set
        cygdrive_flag to CCP_PROC_CYGDRIVE on -U.

        * new-features.xml (ov-new2.4): Document cygpath -U option.
        * utils.xml (cygpath): Ditto.
        * path.xml (func-cygwin-path): Add CCP_PROC_CYGDRIVE description.

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

winsup/cygwin/fhandler_process.cc

@@ -540,7 +540,7 @@ format_process_exename (void *data, char *&destbuf)
     stpcpy (buf, "<defunct>");
   else
     {
-      mount_table->conv_to_posix_path (p->progname, buf, 1);
+      mount_table->conv_to_posix_path (p->progname, buf, CCP_RELATIVE);
       len = strlen (buf);
       if (len > 4)
 	{