libxt: fix build failure

libxt: fix build failure

libxt build fails with this error:

/home/maxin/poky/build/tmp/work/i586-poky-linux/libxt/1_1.1.5-r0/recipe-sysroot/usr/include/bits/long-double.h:57:33:
fatal error: bits/long-double-64.h: No such file or directory
| compilation terminated.
| Makefile:408: recipe for target 'makestrs.o' failed

Fix the makestrs build.

Signed-off-by: Maxin B. John <maxin.john@intel.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>