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

Different Bazel instances can share the zig cache all right.

ci/lint

@@ -7,7 +7,6 @@ set -euo pipefail
 
 cd "$(git rev-parse --show-toplevel)"
 
-
 if command -v shellcheck &> /dev/null; then
     mapfile -t files < \
         <(git ls-files)

ci/test

@@ -5,22 +5,26 @@
 
 set -xeuo pipefail
 
+cache_prefix="${BAZEL_ZIG_CC_CACHE_PREFIX:-/tmp/bazel-zig-cc}"
+
 # check a very hermetic setup with a single target. Re-building all of
 # them takes a long time, so using only one. If we ever decide to build all
 # targets, we will need to exclude Go, since go dynamically links to glibc on
 # linux.
+
 echo "--- build a single target with very hermetic sandbox"
 tools/bazel build "$@" \
     --experimental_use_hermetic_linux_sandbox \
+    --sandbox_writable_path="$cache_prefix" \
     --sandbox_add_mount_pair=/proc \
     //test/c:which_libc_linux_amd64_gnu.2.19
 
 # then test everything else with the standard sandbox
-echo "--- bazel test $@ ..."
+echo "--- bazel test $* ..."
 tools/bazel test "$@" ...
 
 echo "--- ensure github.com/ziglang/zig/issues/13050 does not regress"
-find "${BAZEL_ZIG_CC_CACHE_PREFIX:-/tmp/bazel-zig-cc}" \
+find "$cache_prefix" \
     -name mutex_destructor.o -execdir file '{}' \; \
     | sort \
     | uniq -c \