[embedder] register clang toolchain in workspace.bazel

Change-Id: I1827399eff306d376d8d075d7873de738e2fc0fd
Reviewed-on: https://fuchsia-review.googlesource.com/c/flutter-embedder/+/738382
Reviewed-by: Naud Ghebre <naudzghebre@google.com>
Reviewed-by: Alexander Biggs <akbiggs@google.com>
diff --git a/WORKSPACE.bazel b/WORKSPACE.bazel
index c1d4a1f..a8858de 100644
--- a/WORKSPACE.bazel
+++ b/WORKSPACE.bazel
@@ -50,6 +50,9 @@
     sdk_root_label = "@fuchsia_sdk",
 )
 
+load("@fuchsia_clang//:defs.bzl", "register_clang_toolchains")
+register_clang_toolchains()
+
 # gTest.
 local_repository(
     name = "com_google_googletest",