[Android] Robust fix for missing C++ ABI symbols (__gxx_personality_v0) during static linking

[lparam]

Problem

When building for Android targets using the NDK toolchain, i encountered persistent linker errors (e.g., undefined reference to '__gxx_personality_v0') when attempting to produce fully static binaries.

The root cause is that the NDK's sysroot prioritizes .so stubs over the required static libraries (libc++_static.a, libc++abi.a, libunwind.a). Additionally, the path to libunwind.a is deeply nested within a versioned Clang resource directory, making it difficult to locate
across different NDK versions.

Proposed Solution

I have implemented a robust fix in build.rs that automates the static linking process for Android:

• Dynamic Detection: Automatically detects the Host OS and the NDK's internal Clang version.
• Architecture Mapping: Correctly maps Rust target triples to NDK architectures (e.g., mapping armv7 to arm and i686 to i386).
• Shadow Directory: Creates a temporary directory in OUT_DIR to isolate the correct .a files, ensuring they take precedence during linking.
• Comprehensive Coverage: Supports all major Android architectures: aarch64, armv7, i686, and x86_64.

Impact

This enables boring to produce fully static, portable Android binaries out-of-the-box, without external dependencies on libc++_shared.so.

I have already verified this implementation across all architectures and confirmed it passes CI on multiple host OSes. Let me know if you would like me to submit a PR.