Enable error-prone checks by default

Based on recent work by Dave Borowitz on the Gerrit project [1, 2].

The warnings/error configuration is unchanged, but now the checks are
enabled by default during the build rather than having to be manually
invoked.

[1] https://gerrit-review.googlesource.com/c/gerrit/+/225653
[2] https://gerrit-review.googlesource.com/c/gerrit/+/225714

Change-Id: I112146911d3067bb5283cdf7b188be73f8f8f1e8

.bazelrc

diff --git a/.bazelrc b/.bazelrc
index 765363c..dde54fe 100644
--- a/.bazelrc
+++ b/.bazelrc
@@ -3,6 +3,7 @@
 build --experimental_strict_action_env
 build --action_env=PATH
 build --disk_cache=~/.gerritcodereview/bazel-cache/cas
+build --java_toolchain //tools:error_prone_warnings_toolchain
 
 test --build_tests_only
 test --test_output=errors