[clang] Adding Separate OpenMP Offloading Backend to `libcxx/include/__algorithm/pstl_backends` (PR #66968)

[Louis Dionne via cfe-commits]

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@@ -330,6 +330,23 @@ def getStdFlag(cfg, std):
         default=f"{shlex.quote(sys.executable)} {shlex.quote(str(Path(__file__).resolve().parent.parent.parent / 'run.py'))}",
         help="Custom executor to use instead of the configured default.",
         actions=lambda executor: [AddSubstitution("%{executor}", executor)],
+    ),
+    Parameter(
+        name="openmp_pstl_backend",
+        choices=[True, False],
+        type=bool,
+        default=False,
+        help="Enable the OpenMP compilation toolchain if the PSTL backend was set to OpenMP.",
+        actions=lambda enabled: [
+            AddCompileFlag("-fopenmp"),
+            # The linker needs to find the correct version of libomptarget
+            AddLinkFlag("-Wl,-rpath,%{lib}/../../lib"),
+            AddLinkFlag("-L%{lib}/../../lib"),
+            #  The preprocessor needs to find the omp.h header
+            AddFlag("-I %{lib}/../../runtimes/runtimes-bins/openmp/runtime/src"),
+            # If the OpenMP PSTL backend was enbaled, we wish to run the tests for it
+            AddFeature("openmp_pstl_backend")
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ldionne wrote:

You should take a look at `"_LIBCPP_PSTL_CPU_BACKEND_LIBDISPATCH": "libcpp-pstl-cpu-backend-libdispatch",` and probably enable this feature through `features.py` instead.

https://github.com/llvm/llvm-project/pull/66968