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

[Matt Arsenault 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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arsenm wrote:

The target absolutely should be explicit in any testing files. Pretending these tests can be generic is going to be an intractable problem 

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