fix: use current_thread tokio runtime — avoid pthread_create SEGV on Android

Multi-thread tokio runtime crashes with SEGV_ACCERR in __init_tcb
during pthread_create on Android (static bionic stubs from CRT).
Switch to current_thread runtime which runs network I/O on the
calling thread without spawning additional OS threads.

Also: clean up build.rs — use only libc++_shared.so (dynamic),
remove getauxval_fix.c hack, remove static c++/c++abi linking.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

crates/wzp-android/src/engine.rs

@@ -106,9 +106,9 @@ impl WzpEngine {
             };
         }
 
-        // Create tokio runtime
-        let runtime = tokio::runtime::Builder::new_multi_thread()
-            .worker_threads(2)
+        // Create tokio runtime — use current_thread to avoid pthread_create
+        // issues on Android (SEGV_ACCERR in __init_tcb with multi_thread).
+        let runtime = tokio::runtime::Builder::new_current_thread()
             .thread_name("wzp-net")
             .enable_all()
             .build()?;