[llvm] [libsycl] Add lit configuration files and basic test (PR #177407)

[Kseniya Tikhomirova via llvm-commits]

================
@@ -0,0 +1,85 @@
+## Getting Started
+
+This directory contains `libsycl` tests distributed in subdirectories based on
+testing scope. `libsycl` uses LIT to configure and run its tests.
+
+Please see the [Lit Command Guide](https://llvm.org/docs/CommandGuide/lit.html)
+for more information about LIT.
+
+## Prerequisites
+
+* Target runtime(s) to execute tests on devices.
+  TODO: add link to liboffload instruction once they add it.
+* Compiler & libsycl. Can be built following these
+  [instructions](/libsycl/docs/index.rst).
+
+## Run the tests
+
+`libsycl` is integrated via LLVM_ENABLE_RUNTIMES and is not visible as top
+level target. Same is applicable for tests. To run `check-sycl` tests you
+need to prefix `<build>/runtimes/runtimes-bins/` to the paths of all tests.
----------------
KseniyaTikhomirova wrote:

ok, let's see if Tom will provide feedback.


https://github.com/llvm/llvm-project/pull/177407