[clang] [llvm] [OpenMP] Fix launch_bounds for OpenMP ompx_attribute (PR #195665)

[Johannes Doerfert via cfe-commits]

jdoerfert wrote:

> The original `CreateLaunchBoundsAttr` function checks for the nvptx architecture when `MaxBlocks != nullptr` and nullifies it if the targeting architecture is older than sm_90

Why don't we do that then? Pass nullptr if sm < 90 and avoid the IgnoreArch flag. Am I missing something?

https://github.com/llvm/llvm-project/pull/195665