[roll third_party/pigweed] targets/android: Generic Android target

This creates a Pigweed target for a generic Android device built
against a downloaded Android NDK, the path of which is specified in
the `pw_android_toolchain_NDK_PATH` build arg.

Toolchains for all four supported CPU types (arm, arm64, x64, x86) are
generated, so this can be used with e.g.:

  pw_executable("hello") {
    sources = [ "hello.cc" ]
    deps = dir_pw_log
  ]

  group("android_apps") {
    deps = [
      ":hello(//targets/android:arm_android_debug)",
      ":hello(//targets/android:arm64_android_debug)",
    ]
  }

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/55341

third_party/pigweed Rolled-Commits: 864bbd30af8e54f..6f6a50bbc6816c0
Roller-URL: https://ci.chromium.org/b/8839698898699692656
Cq-Cl-Tag: roller-builder:pigweed-experimental-roller
Cq-Cl-Tag: roller-bid:8839698898699692656
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I537b8446cacd4c922a624bd5b04aa543fb005450
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/56266
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 864bbd3..6f6a50b 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 864bbd30af8e54f7124b3a3fd52ad56dc0f0fb40
+Subproject commit 6f6a50bbc6816c0f41167b7747e97a4475887f66