versioner: Ignore if Clang is missing

This happens in some branches. Work around for now.

Change-Id: I75c01a3ae52ce89f6c56a19728903bf86db0a309
diff --git a/tools/versioner/src/Android.mk b/tools/versioner/src/Android.mk
index dff4f7f..c43a525 100644
--- a/tools/versioner/src/Android.mk
+++ b/tools/versioner/src/Android.mk
@@ -3,8 +3,11 @@
 include $(CLEAR_VARS)
 include $(CLEAR_TBLGEN_VARS)
 
-LLVM_ROOT_PATH := external/llvm
+# Only do this when Clang is available.
 CLANG_ROOT_PATH := external/clang
+ifneq ($(wildcard $(CLANG_ROOT_PATH)/clang.mk),)
+
+LLVM_ROOT_PATH := external/llvm
 include $(CLANG_ROOT_PATH)/clang.mk
 
 LOCAL_MODULE := versioner
@@ -41,3 +44,5 @@
 LOCAL_MODULE_HOST_OS := linux
 
 include $(BUILD_HOST_EXECUTABLE)
+
+endif