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

[Fraser Cormack via cfe-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:

Ach I misunderstood how `update_cc_test_checks` works. It doesn't actually go through the regular LIT infrastructure, so we can't do anything involving custom substitutions to configure which target is being run.

If we wanted to be able to use `update_cc_test_checks` I think we'd need to have every target explicit in every test file, which brings its own inflexibilities and maintenance problems.

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