[roll third_party/pigweed] pw_cpu_exception_cortex_m: Remove packed attributes from structs

Removes the packed attributes from the CpuState structs to ensure they
can be safely directly accessed without a risk of unaligned access to
satisfy `-Werror=address-of-packed-member`.

To ensure it continues to be correct compared to our assembly,
static_asserts were added to verify there is no unexpected padding.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/78184

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 7bb790b97ffe672..09a2f4c76a4a096
Roller-URL: https://ci.chromium.org/b/8825291482996179089
Cq-Cl-Tag: roller-builder:pigweed-sample-project-roller
Cq-Cl-Tag: roller-bid:8825291482996179089
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I2c12fc956de030e135aeb37d4a64f794a0097333
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/sample_project/+/78190
Bot-Commit: Pigweed Integration Roller <pigweed-integration-roller@pigweed.google.com.iam.gserviceaccount.com>
Commit-Queue: Pigweed Integration Roller <pigweed-integration-roller@pigweed.google.com.iam.gserviceaccount.com>
diff --git a/third_party/pigweed b/third_party/pigweed
index 7bb790b..09a2f4c 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 7bb790b97ffe67246cc52a851d36246eb5365b1d
+Subproject commit 09a2f4c76a4a096a80465de590c7fddc2bf52746