libext2fs: fix fsync(2) detection

libext2fs: fix fsync(2) detection

For some reason lib/config.h.in was missing a definition of HAVE_FSYNC
and as a result lib/config.h never had HAVE_FSYNC defined. As a result
we never called fsync(2) for example from
lib/ext2fs/unix_io.c:unix_flush() when we finished creating filesystem
and could miss IO errors happening during creating of the filesystem.
Test generic/405 exposes this problem.

Fix the problem by defining HAVE_FSYNC in lib/config.h.in.

Fixes: f47f31958578
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>