Use plain sh for y.sh, test.sh and clean_all.sh

FreeBSD by default doesn't install bash.

.cirrus.yml

@@ -3,7 +3,7 @@ task:
   freebsd_instance:
     image: freebsd-13-2-release-amd64
   setup_rust_script:
-    - pkg install -y git bash binutils
+    - pkg install -y git binutils
     - curl https://sh.rustup.rs -sSf --output rustup.sh
     - sh rustup.sh --default-toolchain none -y --profile=minimal
   target_cache:

clean_all.sh

@@ -1,4 +1,4 @@
-#!/usr/bin/env bash
+#!/bin/sh
 set -e
 
 rm -rf target/ build_system/target download/ build/ dist/

test.sh

@@ -1,2 +1,2 @@
-#!/usr/bin/env bash
+#!/bin/sh
 exec ./y.sh test "$@"

y.sh

@@ -1,4 +1,4 @@
-#!/usr/bin/env bash
+#!/bin/sh
 
 set -e
 echo "[BUILD] build system" 1>&2