bpo-42336: Improve PCbuild batch files (GH-23275)

(cherry picked from commit 2156d964a12285280c533af1c96eb273c58451e6)

Co-authored-by: Steve Dower <steve.dower@python.org>
diff --git a/PCbuild/env.ps1 b/PCbuild/env.ps1
new file mode 100644
index 0000000..19d7ada
--- /dev/null
+++ b/PCbuild/env.ps1
@@ -0,0 +1,2 @@
+$pcbuild = $script:MyInvocation.MyCommand.Path | Split-Path -parent;
+& cmd /K "$pcbuild\env.bat" $args