Add clang/LLVM 3.5svn support.

Add clang/LLVM 3.5svn support.

The clang/llvm 3.3 has some minor bugs such as the vector ++/-- which
was fixed in 3.4. But the 3.4 version introduces severer OCL bugs as
below:
http://llvm.org/bugs/show_bug.cgi?id=18119
http://llvm.org/bugs/show_bug.cgi?id=18120

It seems that the community will only fix these bugs in the ToT version
rather than the llvm 3.4 branch. I think we'd better to enable clang/llvm
3.5 in beignet. Currently, the 18120 was fixed in ToT, but 18119 still
breaks us. When 18119 get fixed, I will switch the preferred version to
3.5.

Please be noted, when you build clang/llvm 3.5, you need to enable the
cxx11 to make it compatible with beignet.

--enable-cxx11

v2:
fix the llvm3.4 issue.

Signed-off-by: Zhigang Gong <zhigang.gong@intel.com>
Reviewed-by: "Yang, Rong R" <rong.r.yang@intel.com>