[roll third_party/pigweed] pw_cpu_exception: Remove unnecessary forward declaration

Removes a legacy forward declaration of pw_cpu_exception_State by
including pw_cpu_exception/state.h instead which provides that type.

Also updates the Cortex-M backend to expose the C++ type as an opaque
forward declared struct to C.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/76120

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 02c1251de2c4f05..ea719194a262698
Roller-URL: https://ci.chromium.org/b/8827106970055830353
Cq-Cl-Tag: roller-builder:pigweed-sample-project-roller
Cq-Cl-Tag: roller-bid:8827106970055830353
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I226d4de16e62b47501b4fb057dd360730b61cf52
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/sample_project/+/76160
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 02c1251..ea71919 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 02c1251de2c4f0579b3744e0f7dbc56fb65c24e4
+Subproject commit ea719194a262698b1e3383d9e0a4c71f6ea0efbc