Add clang rules for RS_LLVM_* tools.

This change adds new variables for RS_LLVM_* tools, which correspond
to the version of LLVM checked in currently to external/, instead of
mapping to the latest host prebuilts. This will help prevent version
differences for newer IR generated by the updated host prebuilts, which
then might not be readable with the on-device LLVM bits we build from
external/.

Change-Id: I6c7b0fa9082e9c8244cc508cb23960569a057740
diff --git a/core/clang/config.mk b/core/clang/config.mk
index 756bf49..330fd1c 100644
--- a/core/clang/config.mk
+++ b/core/clang/config.mk
@@ -13,6 +13,15 @@
 CLANG_TBLGEN := $(BUILD_OUT_EXECUTABLES)/clang-tblgen$(BUILD_EXECUTABLE_SUFFIX)
 LLVM_TBLGEN := $(BUILD_OUT_EXECUTABLES)/llvm-tblgen$(BUILD_EXECUTABLE_SUFFIX)
 
+# 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 := 3.8
+RS_LLVM_PREBUILTS_BASE := prebuilts/clang/host
+RS_LLVM_PREBUILTS_PATH := $(RS_LLVM_PREBUILTS_BASE)/$(BUILD_OS)-x86/$(RS_LLVM_PREBUILTS_VERSION)/bin
+RS_LLVM_AS := $(RS_LLVM_PREBUILTS_PATH)/llvm-as$(BUILD_EXECUTABLE_SUFFIX)
+RS_LLVM_LINK := $(RS_LLVM_PREBUILTS_PATH)/llvm-link$(BUILD_EXECUTABLE_SUFFIX)
+
 # Clang flags for all host or target rules
 CLANG_CONFIG_EXTRA_ASFLAGS :=
 CLANG_CONFIG_EXTRA_CFLAGS :=