bpo-36941: Windows build changes for Windows ARM64 (GH-13365)

diff --git a/.gitignore b/.gitignore
index 9e60f5a..e3c5809 100644
--- a/.gitignore
+++ b/.gitignore
@@ -70,6 +70,7 @@
 PCbuild/.vs/
 PCbuild/amd64/
 PCbuild/arm32/
+PCbuild/arm64/
 PCbuild/obj/
 PCbuild/win32/
 .purify