Fix Linux fcntl OFD locks for non-LFS architectures (BZ#20251)

[Samuel Thibault]

Just for completeness:

Samuel Thibault, le jeu. 15 nov. 2018 19:53:50 +0100, a ecrit:
> - __USE_LARGEFILE64 is defined, struct flock is kept 32bits, struct
>   flock64 is available as 64bit variant which can be used either with
>   fcntl() with F_*LK64 variants, or with fcntl64.

But with fcntl64 you still have to use F_*LK64 variants, F_*LK variants
still use the 32bit flock structure, right?

Samuel