Swift: Add identify-environment script

swift/tools/BUILD.bazel

@@ -11,9 +11,15 @@ sh_binary(
     srcs = ["autobuild.sh"],
 )
 
+sh_binary(
+    name = "identify-environment",
+    srcs = ["identify-environment.sh"],
+)
+
 pkg_files(
     name = "scripts",
     srcs = [
+        ":identify-environment",
         ":autobuild",
         ":qltest",
     ],

swift/tools/identify-environment.cmd

@@ -0,0 +1,6 @@
+@echo off
+SETLOCAL EnableDelayedExpansion
+
+echo { "swift": { "os": { "name": "macOS" } } }
+
+ENDLOCAL

swift/tools/identify-environment.sh

@@ -0,0 +1,5 @@
+#!/bin/sh
+
+set -eu
+
+echo '{ "swift": { "os": { "name": "macOS" } } }'