[clang] [libclc] [llvm] [libclc] Add initial LIT tests (PR #87989)

[Fraser Cormack via llvm-commits]

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@@ -1,3 +1,6 @@
-__kernel void foo(int *i) {
+// RUN: %clang -emit-llvm -S -o - %s | FileCheck %s
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frasercrmck wrote:

With #146503, clang does at least know about libclc. I've updated this PR to include that one, just to explore how this might work in CI.

I've updated these tests to use `update_cc_test_checks.py`, just on the `amdgcn-mesa-mesa3d` triple for now. There's good and bad to this. I think the good is fairly obvious - thanks for the suggestion - but the downside is that now libclc would ideally be tested every time clang and llvm are modified. I'm not sure whether or not there'll be the appetite for the impact on CI times, let alone on having people have to update the libclc test checks every so often.

We could of course simply *not* test libclc every time clang/llvm are changed, acknowledging that the test checks will go stale and will need to be periodically updated. I'm not sure of the best approach.

https://github.com/llvm/llvm-project/pull/87989