build: fix a bunch of bugs in build script

build.py

@@ -1,9 +1,9 @@
 import argparse
+import os
 import subprocess
 
 platforms = [
     ("darwin", "amd64"),
-    ("darwin", "arm64"),
     ("freebsd", "386"),
     ("freebsd", "amd64"),
     ("freebsd", "arm"),
@@ -29,9 +29,12 @@
                         type=str, help="string used as a version when building binaries")
     args = parser.parse_args()
     version = args.version
-    for (os, arch) in platforms:
+    for (build_os, build_arch) in platforms:
         ext = ""
-        if os == "windows":
+        if build_os == "windows":
             ext = ".exe"
+        build_env = os.environ.copy()
+        build_env["GOOS"] = build_os
+        build_env["GOARCH"] = build_arch
         subprocess.run(["go", "build", "-ldflags", "-X main.version=%s" %
-                        version, "-o", "bombardier-%s-%s%s" % (os, arch, ext)])
+                        version, "-o", "bombardier-%s-%s%s" % (build_os, build_arch, ext)], env=build_env)