vboot_reference: Build host tools conditionally.

Some of the tools and utilities in vboot_reference do not build
with sanitizers enabled. To avoid this, do not build them
when NO_BUILD_TOOLS is defined.

TEST=USE="fuzzer" emerge-amd64-generic vboot_reference does not build host tools
TEST=emerge-falco vboot_reference builds all tools.

Change-Id: If238c98d4058db20765731237153bc6969a06375
Reviewed-on: https://chromium-review.googlesource.com/1060154
Commit-Ready: Manoj Gupta <manojgupta@chromium.org>
Tested-by: Manoj Gupta <manojgupta@chromium.org>
Reviewed-by: Randall Spangler <rspangler@chromium.org>
diff --git a/Makefile b/Makefile
index 995850e..0cd13e2 100644
--- a/Makefile
+++ b/Makefile
@@ -840,8 +840,13 @@
 	$(shell [ -d ${BUILD}/${d} ] || mkdir -p ${BUILD}/${d}))
 # Host targets
+.PHONY: host_tools
+host_tools: utils futil tests
 .PHONY: host_stuff
-host_stuff: utillib hostlib cgpt utils futil tests
+host_stuff: utillib hostlib cgpt \
+	$(if ${NO_BUILD_TOOLS},,host_tools)
 .PHONY: clean