Add a disk cache limit of 100G for bazel (#4893)

Co-authored-by: Jon Ross-Perkins <jperkins@google.com>

.bazelrc

@@ -40,11 +40,10 @@ build --use_target_config_carbon_rules
 # Default to using a disk cache to minimize re-building LLVM and Clang which we
 # try to avoid updating too frequently to minimize rebuild cost. The location
 # here can be overridden in the user configuration where needed.
-#
-# Note that this cache will grow without bound currently. You should
-# periodically run the `scripts/clean_disk_cache.sh` script or some equivalent.
-# https://github.com/bazelbuild/bazel/issues/5139 tracks fixing this in Bazel.
 build --disk_cache=~/.cache/carbon-lang-build-cache
+# If you'd like a different disk cache size, override it by copying this
+# line to `user.bazelrc` in the repository root and modify the number there.
+build --experimental_disk_cache_gc_max_size=100G
 
 # Enable some safety when using the build cache, likely to be defaulted in
 # future Bazel releases.

scripts/clean_disk_cache.sh

@@ -1,22 +0,0 @@
-#!/usr/bin/env bash
-#
-# Part of the Carbon Language project, under the Apache License v2.0 with LLVM
-# Exceptions. See /LICENSE for license information.
-# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-#
-# Clean out any files in the Bazel disk cache which haven't been used for over
-# thirty days.
-
-set -eu
-
-# Default to the same directory in the project `.blazerc`, but you can set this
-# environment variable to override that.
-: ${BAZEL_DISK_CACHE_PATH:=~/.cache/carbon-lang-build-cache}
-
-# As a courtesy, compute and print some approximate stats.
-total_file_count=$(find "$BAZEL_DISK_CACHE_PATH" -type f | wc -l)
-stale_file_count=$(find "$BAZEL_DISK_CACHE_PATH" -type f -atime +30 | wc -l)
-echo "Removing $stale_file_count files out of $total_file_count total."
-
-# Just re-running the find is simpler than managing any state.
-find "$BAZEL_DISK_CACHE_PATH" -type f -atime +30 -delete