[wasm][build] Disable LLVM unwinder in libcxxabi

This change disables the use of llvm libunwind in libcxxabi, which is
enabled by default. This is necessary because the llvm libunwind is not
supported in the WebAssembly target.

Author: kateinoigakukun

utils/swift_build_support/swift_build_support/products/wasisysroot.py

@@ -210,6 +210,7 @@ def _build(self, host_target, enable_wasi_threads=False,
         self.cmake_options.define('LIBCXX_ABI_VERSION', '2')
         self.cmake_options.define('LIBCXXABI_ENABLE_EXCEPTIONS:BOOL', 'FALSE')
         self.cmake_options.define('LIBCXXABI_ENABLE_SHARED:BOOL', 'FALSE')
+        self.cmake_options.define('LIBCXXABI_USE_LLVM_UNWINDER:BOOL', 'FALSE')
         self.cmake_options.define('LIBCXXABI_SILENT_TERMINATE:BOOL', 'TRUE')
         self.cmake_options.define('LIBCXXABI_ENABLE_THREADS:BOOL', cmake_has_threads)
         self.cmake_options.define('LIBCXXABI_HAS_PTHREAD_API:BOOL', cmake_has_threads)