Enable --noexperimental_separate_genfiles_directory

Upstream wants to flip it.  Let's do it before they do to prevent future
breakage.

Change-Id: I1992db8c9f0cd43ba62c1cb627f676a5ac3a3dbd
diff --git a/.bazelrc b/.bazelrc
index 7f7a2ac..c80339f 100644
--- a/.bazelrc
+++ b/.bazelrc
@@ -77,3 +77,5 @@
 # https://github.com/bazelbuild/bazel/issues/6341 for ongoing discussion with
 # upstream about this.
 build --javabase=@openjdk_linux_archive//:jdk --host_javabase=@openjdk_linux_archive//:jdk
+
+build --noexperimental_separate_genfiles_directory