[wasm] Disable building embedded stdlib when cross-compiling for wasm

The stdlib build configuration for wasm is incompatible with the
embedded targets (e.g. `SWIFT_STDLIB_COMPACT_ABSOLUTE_FUNCTION_POINTER=TRUE`),
so we need to disable building the embedded stdlib

Author: kateinoigakukun

utils/swift_build_support/swift_build_support/products/wasmstdlib.py

@@ -90,6 +90,7 @@ def _build(self, host_target, target_triple):
         self.cmake_options.define('SWIFT_STDLIB_TRACING:BOOL', 'FALSE')
         self.cmake_options.define('SWIFT_STDLIB_HAS_ASLR:BOOL', 'FALSE')
         self.cmake_options.define('SWIFT_STDLIB_CONCURRENCY_TRACING:BOOL', 'FALSE')
+        self.cmake_options.define('SWIFT_SHOULD_BUILD_EMBEDDED_STDLIB:BOOL', 'FALSE')
         self.cmake_options.define(
             'SWIFT_STDLIB_INSTALL_PARENT_MODULE_FOR_SHIMS:BOOL', 'FALSE')
         self.cmake_options.define('SWIFT_RUNTIME_CRASH_REPORTER_CLIENT:BOOL', 'FALSE')