[roll third_party/pigweed] pw_libcxx: Add pw_libcxx library

This provides a few symbols whose upstream implementation
is unsuitable for embedded. Instead, we just implement these
symbols by hand, which should just crash if they are ever
reached.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/144970

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 7837bf3c86d47c0..94e41edc059dd6c
Roller-URL: https://ci.chromium.org/b/8766153985214921249
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I2d66fb4a0062a2e181e8035eca12e789b249bbce
Reviewed-on: https://pigweed-review.googlesource.com/c/gonk/+/177897
Bot-Commit: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
Commit-Queue: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
diff --git a/third_party/pigweed b/third_party/pigweed
index 7837bf3..94e41ed 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 7837bf3c86d47c03c00e88f6ad9c2189557b626f
+Subproject commit 94e41edc059dd6c03ddef6b86d26cbb8232ddabf