Force to build llvm from source in 64-bit host build.

Bug: 13751317
Change-Id: I4a4150bfe21607eb7a2342bbd8120b431427eee5
diff --git a/core/clang/config.mk b/core/clang/config.mk
index d44be52..227169d 100644
--- a/core/clang/config.mk
+++ b/core/clang/config.mk
@@ -6,6 +6,11 @@
 WITHOUT_HOST_CLANG := true
 endif
 
+# We don't have 64-bit host prebuilts yet.
+ifeq (true,$(HOST_IS_64_BIT))
+FORCE_BUILD_LLVM_COMPONENTS := true
+endif
+
 LLVM_PREBUILTS_PATH := prebuilts/clang/$(BUILD_OS)-x86/host/3.5/bin
 LLVM_PREBUILTS_HEADER_PATH := prebuilts/clang/$(BUILD_OS)-x86/host/3.5/lib/clang/3.5/include/