RenderScript-specific build updates for LLVM rebase

Bug: http://b/31320715

Use LLVM's RenderScript triples: upstream LLVM now has 32-bit and
64-bit RenderScript triples.  Update RS_TRIPLE build variables to use
the new triples.

Switch prebuilt clang used for building RenderScript runtime library to
the latest prebuilts.

Test: Run RenderScript tests (slang, bcc host tests, RsTest, CTS)

Change-Id: I308f6a2183350cfc380228a1eed07ec118d93a46
diff --git a/core/clang/config.mk b/core/clang/config.mk
index a71f110..60e0641 100644
--- a/core/clang/config.mk
+++ b/core/clang/config.mk
@@ -15,7 +15,7 @@
 # RenderScript-specific tools
 # These are tied to the version of LLVM directly in external/, so they might
 # trail the host prebuilts being used for the rest of the build process.
-RS_LLVM_PREBUILTS_VERSION := clang-2812033
+RS_LLVM_PREBUILTS_VERSION := clang-3289846
 RS_LLVM_PREBUILTS_BASE := prebuilts/clang/host
 RS_LLVM_PREBUILTS_PATH := $(RS_LLVM_PREBUILTS_BASE)/$(BUILD_OS)-x86/$(RS_LLVM_PREBUILTS_VERSION)/bin
 RS_CLANG := $(RS_LLVM_PREBUILTS_PATH)/clang$(BUILD_EXECUTABLE_SUFFIX)