[roll third_party/pigweed] pw_android_toolchain: Generate Android NDK toolchains

The default Pigweed pw_toolchain defines the `ar`, `cc`, and `cxx`
tools in the base toolchain definition, and builds more customization
on top.

For Android, since those paths are defined based on build args and
toolchain defaults such as `current_cpu` and `api_level`, instead
provide "pw_generate_android_toolchain" that defines them last before
calling "generate_toolchain".

Otherwise arrange matters such that defining Android targets feels
as close to the other Pigweed targets as possible.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/55340

third_party/pigweed Rolled-Commits: 6954a8dfa1bb49b..aa00a15bebbb73f
Roller-URL: https://ci.chromium.org/b/8839706515720896336
Cq-Cl-Tag: roller-builder:pigweed-experimental-roller
Cq-Cl-Tag: roller-bid:8839706515720896336
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I4ee95f9e73ceba6a30c0dae7e5d0df2b08859638
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/56261
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 6954a8d..aa00a15 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 6954a8dfa1bb49b9cc9f07254aabaa87a64ef43e
+Subproject commit aa00a15bebbb73f32cf0867a9a15fe7e51815ba1