Explicitly check for ftruncate64() in configure.in

Apparently Mac OS 10.5 defines fstat64(), but not ftruncate64(),
causing resize2fs to fail to build.  So check explicitly for
ftruncate64(), and fall back to ftruncate() if necessary.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
diff --git a/configure b/configure
index 4ab9e94..6cda01c 100755
--- a/configure
+++ b/configure
@@ -14860,7 +14860,8 @@
 
 
 
-for ac_func in chflags getrusage llseek lseek64 open64 fstat64 getmntinfo strtoull strcasecmp srandom jrand48 fchown mallinfo fdatasync strnlen strptime strdup sysconf pathconf posix_memalign memalign valloc __secure_getenv prctl mmap utime setresuid setresgid
+
+for ac_func in chflags getrusage llseek lseek64 open64 fstat64 ftruncate64 getmntinfo strtoull strcasecmp srandom jrand48 fchown mallinfo fdatasync strnlen strptime strdup sysconf pathconf posix_memalign memalign valloc __secure_getenv prctl mmap utime setresuid setresgid
 do
 as_ac_var=`echo "ac_cv_func_$ac_func" | $as_tr_sh`
 { echo "$as_me:$LINENO: checking for $ac_func" >&5