Actually do metadce in at least one variant of test_metadce_cxx. NFC (#22429)

With `-O2` we were not actually running metadce.

Author: sbc100

test/other/metadce/test_metadce_cxx_lto.exports

@@ -1,14 +1,5 @@
-__cxa_increment_exception_refcount
-__indirect_function_table
-__wasm_call_ctors
-_emscripten_stack_alloc
-_emscripten_stack_restore
-_emscripten_timeout
-dynCall_iiiiiijj
-dynCall_iiiiij
-dynCall_iiiiijj
-dynCall_jiji
-dynCall_viijii
-emscripten_stack_get_current
-main
-memory
+m (memory)
+n (__wasm_call_ctors)
+o (main)
+p (_emscripten_timeout)
+q (__indirect_function_table)

test/other/metadce/test_metadce_cxx_lto.gzsize

@@ -1 +1 @@
-8661
+8423

test/other/metadce/test_metadce_cxx_lto.imports

@@ -1,13 +1,12 @@
-env._abort_js
-env._emscripten_memcpy_js
-env._emscripten_runtime_keepalive_clear
-env._setitimer_js
-env._tzset_js
-env.emscripten_resize_heap
-wasi_snapshot_preview1.environ_get
-wasi_snapshot_preview1.environ_sizes_get
-wasi_snapshot_preview1.fd_close
-wasi_snapshot_preview1.fd_read
-wasi_snapshot_preview1.fd_seek
-wasi_snapshot_preview1.fd_write
-wasi_snapshot_preview1.proc_exit
+a (fd_seek)
+b (emscripten_resize_heap)
+c (_tzset_js)
+d (_setitimer_js)
+e (_emscripten_runtime_keepalive_clear)
+f (_abort_js)
+g (proc_exit)
+h (fd_write)
+i (fd_read)
+j (fd_close)
+k (environ_sizes_get)
+l (environ_get)

test/other/metadce/test_metadce_cxx_lto.jssize

@@ -1 +1 @@
-21141
+20434

test/other/metadce/test_metadce_cxx_lto.sent

@@ -1,13 +1,12 @@
-_abort_js
-_emscripten_memcpy_js
-_emscripten_runtime_keepalive_clear
-_setitimer_js
-_tzset_js
-emscripten_resize_heap
-environ_get
-environ_sizes_get
-fd_close
-fd_read
-fd_seek
-fd_write
-proc_exit
+a (fd_seek)
+b (emscripten_resize_heap)
+c (_tzset_js)
+d (_setitimer_js)
+e (_emscripten_runtime_keepalive_clear)
+f (_abort_js)
+g (proc_exit)
+h (fd_write)
+i (fd_read)
+j (fd_close)
+k (environ_sizes_get)
+l (environ_get)

test/other/metadce/test_metadce_cxx_lto.size

@@ -1 +1 @@
-129045
+122726

test/test_other.py

@@ -8689,7 +8689,7 @@ def test_metadce_minimal_pthreads(self):
     'ctors1':    (['-O2', '-sEVAL_CTORS'],   [], ['waka']),
     'ctors2':    (['-O2', '-sEVAL_CTORS=2'], [], ['waka']),
     'wasmfs':    (['-O2', '-sWASMFS'],       [], ['waka']),
-    'lto':       (['-O2', '-flto'],       [], ['waka']),
+    'lto':       (['-Oz', '-flto'],          [], ['waka']),
   })
   def test_metadce_cxx(self, *args):
     # do not check functions in this test as there are a lot of libc++ functions