configure: Remove cl_khr_fp64 for device that don't support doubles

Also remove definitions if provided by clang (3.7+)
This halves the size of builtin.opt.{cedar,barts}.bc

reviewer: tstellard
Signed-off-by: Jan Vesely <jan.vesely@rutgers.edu>

git-svn-id: https://llvm.org/svn/llvm-project/libclc/trunk@260303 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed