fuchsia: Let linker know where to find libclang_rt.builtin.a

BUG=724204
R=scottmg@chromium.org

Review-Url: https://codereview.chromium.org/2895583004 .
Cr-Original-Commit-Position: refs/heads/master@{#473292}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 7d38657a69469a0c14213e9be65bfe1d682abef2

config/fuchsia/BUILD.gn

@@ -2,6 +2,7 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+import("//build/config/fuchsia/config.gni")
 import("//build/config/sysroot.gni")
 
 assert(is_fuchsia)
@@ -22,6 +23,15 @@ config("compiler") {
   }
   asmflags = cflags
 
+  # TODO(thakis): Once Fuchsia's libclang_rt.builtin no longer has upstream
+  # patches, we might want to make tools/clang/scripts/update.py build it
+  # and bundle it with the clang package instead of using the library from
+  # the SDK, https://crbug.com/724204
+  ldflags += [
+    "-resource-dir",
+    rebase_path(fuchsia_sdk, root_build_dir) + "/toolchain_libs/clang/5.0.0",
+  ]
+
   libs = [
     "mxio",
     "magenta",