Include libclang_rt.builtins.a for Fuchsia

Based on https://codereview.chromium.org/2897463003/.

Test: Run update.py --force-local-build, remove https://cs.chromium.org/chromium/src/build/config/fuchsia/BUILD.gn?l=41 and referenced files, and rebuild some Fuchsia binaries
Test: Run package.py and verify the .a's are included.
Bug: 724204
Change-Id: If1492138829846a0f970d034f28a84d517554401
Reviewed-on: https://chromium-review.googlesource.com/1211879
Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Scott Graham <scottmg@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#590521}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 9fc3a5c27d64ef9eedb31d33ad09da9e6a98f6d7

config/fuchsia/BUILD.gn

@@ -30,16 +30,6 @@ config("compiler") {
   asmflags = cflags
 
   ldflags += [
-    # 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
-    # Note: Intentionally 8.0.0 instead of $clang_version because the clang
-    # version of the toolchain_libs directory in the Fuchsia SDK can be
-    # different from the version of Chromium's clang.
-    "-resource-dir",
-    rebase_path(fuchsia_sdk, root_build_dir) + "/toolchain_libs/clang/8.0.0",
-
     # The stack defaults to 256k on Fuchsia (see
     # https://fuchsia.googlesource.com/zircon/+/master/system/private/zircon/stack.h#9),
     # but on other platforms it's much higher, so a variety of code assumes more