roll: third_party/pigweed 4 commits

9c64c8d1cd1cec4 pw_cpu_exception_cortex_m: Make PC LR optional
a98647d744dc24c pw_toolchain: Add linux_sysroot.bzl
7dc26abc274fa80 pw_libcxx: Actually implement operator delete
b2afd53cde2dcc9 pw_ide: Revise docs

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 510f3669f3efa06..9c64c8d1cd1cec4
Roller-URL: https://ci.chromium.org/b/8742140503151709569
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: Idd275436e491670e883e3a21ff80c8b7f7fbc9d9
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/223797
Commit-Queue: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
Lint: Lint 🤖 <android-build-ayeaye@system.gserviceaccount.com>
Bot-Commit: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
diff --git a/third_party/pigweed b/third_party/pigweed
index 510f366..9c64c8d 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 510f3669f3efa061b36ca84166b5c2d20118eccb
+Subproject commit 9c64c8d1cd1cec45d0f6ebbe13f19646421d6a9b