[infra] Roll clang to match the version used by Flutter

build/toolchain/android/BUILD.gn

Index: build/toolchain/android/BUILD.gn
diff --git a/build/toolchain/android/BUILD.gn b/build/toolchain/android/BUILD.gn
index 5e4847349d11342271e9d3ed8f7737de1e5f5372..51f03206088698eaa4a4fd1febb980c4401ce277 100644
--- a/build/toolchain/android/BUILD.gn
+++ b/build/toolchain/android/BUILD.gn
@@ -47,17 +47,27 @@ template("android_gcc_toolchain") {
 
     is_clang = invoker.is_clang
     if (is_clang) {
-      prefix = rebase_path("//third_party/llvm-build/Release+Asserts/bin",
+      host_suffix = ""
+      if (host_os == "linux") {
+        host_suffix = "x86_64-linux"
+      } else if (host_os == "mac") {
+        host_suffix = "x86_64-darwin"
+      } else {
+        assert(false, "Unknown host")
+      }
+
+      prefix = rebase_path("//buildtools/toolchain/clang+llvm-$host_suffix/bin",
                            root_build_dir)
 
       cc = compiler_prefix + prefix + "/clang"
       cxx = compiler_prefix + prefix + "/clang++"
+      ar = prefix + "/llvm-ar"
     } else {
       cc = compiler_prefix + tool_prefix + "gcc"
       cxx = compiler_prefix + tool_prefix + "g++"
+      ar = tool_prefix + "ar"
     }
 
-    ar = tool_prefix + "ar"
     ld = cxx
     readelf = compiler_prefix + tool_prefix + "readelf"
     nm = compiler_prefix + tool_prefix + "nm"