bpo-35976: Enable Windows projects to build with platform ARM32 (GH-11825)

This change adds the necessary items to the build projects to avoid erroring out right at the start. It does not add _support_ for targeting Windows on ARM32, but is a necessary prerequisite for adding it.
diff --git a/.gitignore b/.gitignore
index 215d7f5..7ee9e6d 100644
--- a/.gitignore
+++ b/.gitignore
@@ -69,6 +69,7 @@
 PCbuild/*.VC.opendb
 PCbuild/.vs/
 PCbuild/amd64/
+PCbuild/arm32/
 PCbuild/obj/
 PCbuild/win32/
 .purify