lsfd: use constants defined in asm/fctl.h flags field of a fdinfo

lsfd: use constants defined in asm/fctl.h flags field of a fdinfo

Close #1709.

The original code decoded the field using constants defined in
/usr/include/fcntl.h. The constants defined in /usr/include/fcntl.h
was suitable for passing to the kernel as a part of arguments of
system calls like open(2). However, they were not suitable for
decoding the field.

Let's think about decoding 0300000 in

    $ cat /proc/157067/fdinfo/3
    pos:	0
    flags:	0300000
    $ lsfd -p 157067 -o+flags -Q -Q 'ASSOC == "3"'
    COMMAND       PID USER ASSOC MODE TYPE SOURCE MNTID INODE NAME               FLAGS
    test_mkfds 125128  jet     3  r--  DIR   dm-0    96    96 /    ???????????????????

The decoded string is printed at ???????????????????.

Quoted from /usr/include/bits/fcntl-linux.h:

    #ifndef __O_LARGEFILE
    # define __O_LARGEFILE	0100000
    #endif
    #ifndef __O_DIRECTORY
    # define __O_DIRECTORY	0200000
    #endif
    #ifndef __O_TMPFILE
    # define __O_TMPFILE   (020000000 | __O_DIRECTORY)
    #endif
    ...
    #ifdef __USE_XOPEN2K8
    # define O_DIRECTORY	__O_DIRECTORY	/* Must be a directory.  */
    ...
    #endif
    ...
    #ifdef __USE_LARGEFILE64
    # define O_LARGEFILE __O_LARGEFILE
    #endif

With these constants, 0300000 is decoded as "directory,_tmpfile" or
"largefile,directory,_tmpfile".

Unexpectedly the decoded string has "_tmpfile".
It has "largefile" only when we define __USE_LARGEFILE64 when building
lsfd though it should have "largefile" always.

Quoted from /usr/include/asm-generic/fcntl.h:

    #ifndef O_LARGEFILE
    #define O_LARGEFILE	00100000
    #endif
    #ifndef O_DIRECTORY
    #define O_DIRECTORY	00200000	/* must be a directory */
    #endif
    #ifndef __O_TMPFILE
    #define __O_TMPFILE	020000000
    #endif

The decoded string is "largefile,directory". It doesn't depend on
__USE_LARGEFILE64.

This change adds lsfd-decode-file-flags.c, a new small and isolated
source file, in which lsfd_decode_file_flags(), the function for
decoding the field is defined.

include/c.h includes /usr/include/fcntl.h. Almost all lsfd related
source files includes include/c.h indirectly. On the other hand,
lsfd-decode-file-flags.c includes only /usr/include/asm-generic/fcntl.h
or /usr/include/asm/fcntl.h. So the function can decode the field
expectedly.

Signed-off-by: Masatake YAMATO <yamato@redhat.com>