Add sycl headers to bazel toolchain config for DPCPP through icx (#2905)

* add required sycl linkage when probing for include paths

* add sycl linkage only when using dpc

dev/bazel/toolchains/cc_toolchain_lnx.bzl

@@ -128,7 +128,8 @@ def _preapre_builtin_include_directory_paths(repo_ctx, tools):
             tools.dpcc,
             "-xc++",
             get_no_canonical_prefixes_opt(repo_ctx, tools.dpcc) +
-            _add_gcc_toolchain_if_needed(repo_ctx, tools.dpcc),
+            _add_gcc_toolchain_if_needed(repo_ctx, tools.dpcc) +
+            _add_sycl_linkage(repo_ctx, tools.dpcc) if tools.is_dpc_found else [],
         ) +
         required_tmp_includes,
     )
@@ -154,6 +155,12 @@ def _add_gcc_toolchain_if_needed(repo_ctx, cc):
     else:
         return []
 
+def _add_sycl_linkage(repo_ctx, cc):
+    if ("icx" in cc) or ("icpx" in cc):
+        return ["-fsycl"]
+    else:
+        return []
+
 def configure_cc_toolchain_lnx(repo_ctx, reqs):
     if reqs.os_id != "lnx":
         auto_configure_fail("Cannot configure Linux toolchain for '{}'".format(reqs.os_id))