This library depends on a snapshot of LLVM that only works with C++11.

Bug: http://b/111067277
Test: Build with default cpp_std as C++17.
Change-Id: I40de7e2357afa3c16ceac7f50241a6d0437aba09
Reviewed-on: https://swiftshader-review.googlesource.com/c/22628Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Tested-by: Stephen Hines <srhines@google.com>