Fix configure error in large file checks on 64-bit architectures

 configure:17888: checking for native large file support
 configure:17891: error: in `/home/jenkins/oe/shr-core-branches/shr-core/tmp-eglibc/work/core2-64-oe-linux/libimobiledevice/1.1.4-r0/libimobiledevice-1.1.4':
 configure:17893: error: cannot run test program while cross compiling

configure.ac was using AC_SYS_LARGEFILE macro as is typical, but then
there was an extra runtime check added beyond that:
check if off_t is 8 bytes (64 bits) long.
If that runtime check passed, _FILE_OFFSET_BITS was defined as 64.

Runtime checks need to go away for cross compiling, and luckily this extra
check was not serving any useful purpose. Note that off_t was *already*
64 bits, *without* setting _FILE_OFFSET_BITS, which makes _FILE_OFFSET_BITS
unneeded for large file support. 

If AC_SYS_LARGEFILE macro sets ac_cv_sys_file_offset_bits=no,
just leave _FILE_OFFSET_BITS undefined!

--- libimobiledevice-1.1.4/configure.ac.old	2015-07-15 01:38:50.900143927 -0700
+++ libimobiledevice-1.1.4/configure.ac	2015-07-15 01:39:13.300144430 -0700
@@ -174,16 +174,6 @@
 if test "$enable_largefile" != no; then
     if test "$ac_cv_sys_file_offset_bits" != 'no'; then
 	LFS_CFLAGS="$LFS_CFLAGS -D_FILE_OFFSET_BITS=$ac_cv_sys_file_offset_bits"
-    else
-	AC_MSG_CHECKING(for native large file support)
-	AC_RUN_IFELSE([AC_LANG_SOURCE([#include <unistd.h>
-	  int main (int argc, char **argv)
-	  {
-	      exit(!(sizeof(off_t) == 8));
-	  }])],
-	[ac_cv_sys_file_offset_bits=64; AC_DEFINE(_FILE_OFFSET_BITS,64)
-	 AC_MSG_RESULT(yes)],
-	[AC_MSG_RESULT(no)])
     fi
     if test "$ac_cv_sys_large_files" != 'no'; then
 	LFS_CFLAGS="$LFS_CFLAGS -D_LARGE_FILES=1"