libext2fs: use HAVE_FSTAT64 instead of HAVE_STAT64 for ext2fs_stat()

libext2fs: use HAVE_FSTAT64 instead of HAVE_STAT64 for ext2fs_stat()

Commit 6b56f3d92d introduced the use of HAVE_STAT64 without arranging
that it be defined in configure.in.  Previously ext4.h used
HAVE_OPEN64, but apparently there are (broken) platforms that have
open64() but not stat64().  Go figure.

We do need to consistently use a single test for ext2fs_stat(),
ext2fs_fstat(), and struct ext2fs_struct_stat, or we could end up
passing a struct stat64 to a fstat() system call, or some such.  I've
elected to use HAVE_FSTAT64 because: (a) it's already defined in the
configure script, and (b) if we ever come across a really broken
platform that defines fstat64() but not stat64(), we can always
emulate stat64() using open64() followed by a fstat64().

This commit fixed a bug whose symptoms were that mke2fs would not work
if given a file > 2GB on 32-bit platforms.

Addresses-Debian-Bug: #647245

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>