[roll third_party/pigweed] pw_build: Disable deprecated pragma warnings

Use of non ISO standard C++ pragmas are warned by the latest Clang
toolchain which blocks the clang roll. Temporarily disabling these
warnings and filed a tracking bug to fix usages.

Original-Bug: b/335328444, b/333448202
Docs: N/A
Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/203856

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: a4dd94c7fc90cf4..c779ef6691f3de7
Roller-URL: https://ci.chromium.org/b/8750384891503773425
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I6b1ecfd85eaca9b8a32730472a4a35b3989944b3
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/quickstart/bazel/+/204170
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 a4dd94c..c779ef6 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit a4dd94c7fc90cf44581b35487b4a2b0c3aae5299
+Subproject commit c779ef6691f3de734cd70447d5f29e56dcc7cd8f