[SPIR-V] Add builtin/intrinsic for subgroup ballot (#174862)

Summary:
This patch adds an LLVM intrinsic and lowering for a subgroup ballot and
a corresponding clang builtin. This uses the already present support but
provides in a way accessible to other targets. With this and
https://github.com/llvm/llvm-project/pull/174655 we should be able to
most of the basic functions, like shuffling, active masks, and
reductions. More work will be needed for canonicalizing / exposing the
SPIR-V functions, but these are the fundamental builtins I need.

0 files changed, 0 insertions, 0 deletions