Build the default library for Android

[ASDAlexander77]

What

scripts/build_android.bat [abi] [release|debug] [gc|rc|none] builds the default library for Android API 29 on a Windows host with the Android NDK. It's the Android counterpart of scripts/build.sh; with no arguments it builds every combination: arm64-v8a and x86_64, release and debug, gc/rc/none. For each ABI it stages one complete tree:

__build/android/<abi>/defaultlib/lib/<mode>/<model>/libTypeScriptDefaultLib.a
__build/android/<abi>/defaultlib/dll/<mode>/<model>/libTypeScriptDefaultLib.so
__build/android/<abi>/defaultlib/*.d.ts ...

A program for that ABI passes --default-lib-path=__build/android/<abi>. The C++ wrappers are compiled with NDK clang++, lib.ts and lib.linux.ts with tslang -mtriple=<arch>-linux-android29, and both are archived with NDK llvm-ar.

Differences from build.sh:

• No curl. Android has no libcurl, so HTTP is the new src/wrappers/http_stub.cpp: the same http_* functions as http_linux.cpp, with every request failing (errorCode -1), so fetch() throws. There's therefore no linker script pulling in -lcurl; the archive is the library itself.
• Everything is PIC, the archive too: Android executables must be PIE.
• The .so links libc++_shared.so, which the app ships (Android allows one C++ runtime per app). Under gc, GC_* stay undefined in it on purpose, as in build.sh.

API 29 is the floor: lib.linux.ts calls timespec_get, which Android's libc has from 29 on. The README gets an Android section with a full compile-and-link example.

Needs ASDAlexander77/TypeScriptCompiler#507 for the Android collector and async runtime (it fixes the standalone runtime project, which lacked GC_enable_threads). It also needs a tslang with ASDAlexander77/TypeScriptCompiler#506 (TOOL_PATH, default: the compiler's release build tree). Tested with NDK r30.

Verification

• All 12 configurations build.
• A test program (class, assert, number to string, Date, async/await, fetch) was linked with NDK clang++ -pie -static-libstdc++ against these archives. That ran for both ABIs, under gc, rc and none (release), and gc (debug):
  • all 8 link;
  • the dynamic dependencies are libc, libm and libdl only;
  • the stub http_request is linked in;
  • rc and none contain no GC_*.
• The .so's undefined symbols all resolve against the API 29 Bionic stubs, except two kinds:
  • GC_* under gc, which is intended.
  • A weak memfd_create (API 30) on arm64. It comes from the NDK's own libclang_rt.builtins (aarch64.c.o), not from this library. Because it's weak, it resolves to null on 29.
• Link-only: no Android device or emulator was available, so nothing has been run.

Noticed, not changed

• lib.linux.ts declares struct tm as nine i32s (36 bytes), but it's 56 bytes on 64-bit Linux and Android (tm_gmtoff, tm_zone). So gmtime_r and localtime_r write past the tuple, on Linux too.
• The fetch error message says "WinHTTP" on every platform.

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