Turn off host tool build warnings

We probably can't fix those warnings from the upstream/generated code.
Turn off the warnings to reduce the build warning noise.

Change-Id: Ifcc0a09b28bfb858cffd4f553c432768f388fd19

.bazelrc

diff --git a/.bazelrc b/.bazelrc
index 7ff5627..c4e0831 100644
--- a/.bazelrc
+++ b/.bazelrc
@@ -2,3 +2,8 @@
 
 # Disable the low signal-to-noise ratio warnings
 build --copt=-Wno-unused-function
+
+# Disable tool build warnings. The tools are fetched/generated from OSS repos
+build --host_copt=-Wno-unused-variable
+build --host_copt=-Wno-unused-value
+build --host_copt=-Wno-uninitialized