Update to clang-r353983.

Test: prebuilt/clang-tools/build-prebuilts.sh
Change-Id: I38ebf458e5a873610db6726d508f114b1e3061c1
diff --git a/build-prebuilts.sh b/build-prebuilts.sh
index f46beca..f8e2cba 100755
--- a/build-prebuilts.sh
+++ b/build-prebuilts.sh
@@ -15,8 +15,8 @@
 # limitations under the License.
 
 export LLVM_BUILD_HOST_TOOLS=true
-export LLVM_PREBUILTS_VERSION=clang-r349610
-export LLVM_RELEASE_VERSION=8.0.8
+export LLVM_PREBUILTS_VERSION=clang-r353983
+export LLVM_RELEASE_VERSION=9.0.1
 
 # FIXME: Workaround to build bionic versioner in the aosp/clang-tools branch.
 export FORCE_BUILD_LLVM_COMPONENTS=true