[roll third_party/pigweed] pw_polyfill: Split up the polyfill targets

Splits up the build rules for the polyfill targets to get ready
for explicit polyfill dependencies in Pigweed libraries instead of
relying on a blanket polyfill across the board.

Original-Bug: 602
Original-Bug: 603
Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/78587

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 20fbb55dfe06a3f..a0fc38ce53e80a2
Roller-URL: https://ci.chromium.org/b/8824614101569154433
Cq-Cl-Tag: roller-builder:pigweed-sample-project-roller
Cq-Cl-Tag: roller-bid:8824614101569154433
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: Idd797bc761fe2c9d46e7dea5ca7372dbf62666e6
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/sample_project/+/79321
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 20fbb55..a0fc38c 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 20fbb55dfe06a3f8f14043b55e65bfa3c300de95
+Subproject commit a0fc38ce53e80a20c5aa24c197b368040e07d692