[SYCL] Disable self-contained-headers test on Windows (#19973)

The test is flaky and has no value in general.

---------

Co-authored-by: Andrei Elovikov <andrei.elovikov@intel.com>

Author: bader

sycl/test/self-contained-headers/lit.local.cfg

@@ -7,8 +7,4 @@ config.test_format = SYCLHeadersTest()
 # standalone. `os.path.join` is required here so the filtering works
 # cross-platform
 config.sycl_headers_xfail = [
-    # FIXME: remove this rule when the header is moved to the clang project
-    os.path.join(
-        "sycl", "stl_wrappers", "__sycl_cmath_wrapper_impl.hpp"
-    ),
 ]

sycl/test/self-contained-headers/sycl/stl_wrappers/__sycl_cmath_wrapper_impl.hpp.cpp

@@ -0,0 +1,11 @@
+// RUN: %clangxx -fsycl -fsyntax-only -Xclang -verify %s
+// expected-no-diagnostics
+//
+// XFAIL: !system-windows
+// UNSUPPORTED: system-windows
+// Different versions of STL implementations by Microsoft either implicitly
+// include cmath or not. It means the test result depends on the system
+// environment.
+
+// TODO: Longer term that header should really be moved to the clang project.
+#include <sycl/stl_wrappers/__sycl_cmath_wrapper_impl.hpp>