Only build HOST Clang when forced to do so.

Bug: 10653601
Change-Id: I7e8ac24927ee4c97d560ca8281c5cf48399ca24b
diff --git a/host_shared_clang.mk b/host_shared_clang.mk
index f2ce5a9..d4ec63c 100644
--- a/host_shared_clang.mk
+++ b/host_shared_clang.mk
@@ -1,3 +1,5 @@
+# Don't build the library unless forced to.
+ifeq (true,$(FORCE_BUILD_LLVM_COMPONENTS))
 # Don't build the library in unbundled branches.
 ifeq (,$(TARGET_BUILD_APPS))
 
@@ -33,4 +35,5 @@
 include $(CLANG_HOST_BUILD_MK)
 include $(BUILD_HOST_SHARED_LIBRARY)
 
-endif # don't build in unbundled branches
\ No newline at end of file
+endif # don't build in unbundled branches
+endif # don't build unless forced to