Update bazel to fix some Incompatible Target Skipping bugs

This is the same version as 4.0.0rc2 except with 2 cherry-picks:
a3c94ec2ed Fix builds for filegroup targets with incompatible dependencies
b3c9d7381c Fix a couple of bugs with Incompatible Target Skipping

The patch for the filegroup fix has already merged on master:
bazelbuild/bazel#12601

The other patch is still under review:
bazelbuild/bazel#12560

This should enable us to convert the code base to use platforms.

Change-Id: I35f078c2576f5268d5e3fb33e9bd86732529f744

tools/bazel

@@ -24,7 +24,7 @@ if [[ -n "${BAZEL_OVERRIDE+x}" ]]; then
   exec "${BAZEL_OVERRIDE}" "$@"
 fi
 
-readonly VERSION="4.0.0rc2-202011211956+37a429ad12"
+readonly VERSION="4.0.0rc2-202012022031+a3c94ec2ed"
 
 readonly DOWNLOAD_DIR="${HOME}/.cache/bazel"
 # Directory to unpack bazel into.  This must change whenever bazel changes.