[roll third_party/pigweed] pw_build: Avoid importing pty on Windows

The pw-wrap-ninja command relies on pty for intercepting and parsing
Ninja output. This doesn't work on Windows, so on Windows the script
simply runs Ninja without any wrapper.

As it turns out, the 'pty' module, while existing on Windows, breaks if
you attempt to actually import it. Since this module isn't used in the
script when it runs on Windows anyways, this commit guards its import
behind a platform check.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/126941

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 98578de84dcbf93..49f9451b35b4c02
Roller-URL: https://ci.chromium.org/b/8790864454709007697
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I8f1e0a81fdeca8c6ccfc61842b77b382f74ee97f
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/126980
Commit-Queue: Pigweed Integration Roller <pigweed-integration-roller@pigweed.google.com.iam.gserviceaccount.com>
Bot-Commit: Pigweed Integration Roller <pigweed-integration-roller@pigweed.google.com.iam.gserviceaccount.com>
diff --git a/third_party/pigweed b/third_party/pigweed
index 98578de..49f9451 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 98578de84dcbf93825a9675fe8c92cadb1101177
+Subproject commit 49f9451b35b4c02f7431b5b99a67087c05573160