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

[Matt Arsenault via cfe-commits]

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

It is essential that clang should know about libclc. libclc exists purely as an extension of the compiler. From the user perspective the opencl builtin library is invisible and always available, which requires clang to handle it without any additional user configuration 

Ideally it should universally be available in the clang resource directory 

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