build(deps): bump third_party/icestorm from `d20a5e9` to `1a40ae7` (#3503)

Bumps [third_party/icestorm](https://github.com/YosysHQ/icestorm) from `d20a5e9` to `1a40ae7`.
- [Commits](https://github.com/YosysHQ/icestorm/compare/d20a5e9001f46262bf0cef220f1a6943946e421d...1a40ae75d4eebee9cce73a2c4d634fd42ed0110f)

---
updated-dependencies:
- dependency-name: third_party/icestorm
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
diff --git a/third_party/icestorm b/third_party/icestorm
index d20a5e9..1a40ae7 160000
--- a/third_party/icestorm
+++ b/third_party/icestorm
@@ -1 +1 @@
-Subproject commit d20a5e9001f46262bf0cef220f1a6943946e421d
+Subproject commit 1a40ae75d4eebee9cce73a2c4d634fd42ed0110f