all commands: use /tmp/bazel-zig-cc (#6)

Different Bazel instances can share the zig cache all right.

.buildkite/pipeline.yml

@@ -3,15 +3,11 @@
 
 steps:
   - label: "Test"
-    command: |
-      . .buildkite/setup-bazelrc.sh
-      ci/test
+    command: ci/test
   - label: "Lint"
-    command: |
-      . .buildkite/setup-bazelrc.sh
-      ci/lint
+    command: ci/lint
   - label: "List Platforms"
-    command: "ci/list_toolchains_platforms"
+    command: ci/list_toolchains_platforms
   - label: "Test Release and Launcher scripts"
     command: |
       git config --global user.email "buildkite@example.com"
@@ -31,7 +27,6 @@ steps:
       ci/launcher-wine64
   - label: "mod-tidy and update-repos"
     command: |
-      . .buildkite/setup-bazelrc.sh
       bin/mod-tidy
       git diff --exit-code
 agents:

.buildkite/setup-bazelrc.sh

@@ -1,15 +0,0 @@
-# Copyright 2023 Uber Technologies, Inc.
-# Licensed under the Apache License, Version 2.0
-
-if [ -z "${BUILDKITE_BUILD_NUMBER:-}" ]; then
-    >&2 echo "error: expected to run in buildkite"
-    exit 1
-fi
-
-export BAZEL_ZIG_CC_CACHE_PREFIX="/tmp/bazel-zig-cc${BUILDKITE_BUILD_NUMBER}"
-mkdir -p "$BAZEL_ZIG_CC_CACHE_PREFIX"
-
-cat > .custom.ci.bazelrc <<EOF
-common --repo_env BAZEL_ZIG_CC_CACHE_PREFIX="$BAZEL_ZIG_CC_CACHE_PREFIX"
-build --sandbox_writable_path "$BAZEL_ZIG_CC_CACHE_PREFIX"
-EOF