[roll third_party/pigweed] pw_toolchain/cmake: Update GCC & Clang toolchain backends

Extends the backend selection for the GCC and Clang CMake
toolchains to get closer to GN parity.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/79964

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 2d7958dc6e68cab..4aa99d0ae3c517e
Roller-URL: https://ci.chromium.org/b/8824391340676580273
Cq-Cl-Tag: roller-builder:pigweed-experimental-roller
Cq-Cl-Tag: roller-bid:8824391340676580273
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I885bb41f6a40d6422c168f6ee254ce98420a9f0b
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/80830
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 2d7958d..4aa99d0 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 2d7958dc6e68cab5f1837e3ccde1627eda9aeb8f
+Subproject commit 4aa99d0ae3c517ef06eb9a966f85022f68e10859