Clang-11 support

[dcampora]

LLVM and clang have undergone several updates in critical areas that improve the support of the C++ standard and the general performance of the compiled code. The current status of the readme reflects the steps to make compilation with clang-8 work, although work has continued in the SPIRV-LLVM-Translator and pocl with releases that mark clang-11.

It would be great to know what the steps would be to bring hipcl up to speed with clang-11, and what would be the required effort to maintain support for it going forward.

[franz]

The hipcl library code should be mostly independent of the clang/LLVM version, what needs to be done is someone forward-porting the Clang 8 patches which were done as part of hipcl work.