Fix build with LLVM 3.5

Reviewed-by: Aaron Watry <awatry@gmail.com>

git-svn-id: https://llvm.org/svn/llvm-project/libclc/trunk@198167 91177308-0d34-0410-b5e6-96231b3b80d8
Pass -fno-builtin flag to clang to silence warnings

Reviewed-by: Aaron Watry <awatry@gmail.com>

git-svn-id: https://llvm.org/svn/llvm-project/libclc/trunk@198168 91177308-0d34-0410-b5e6-96231b3b80d8