Fix test_utf32. NFC (emscripten-core#22698)

This test was never actually being run with `-fshort-wchar` because it
was being passed as `args` rather than `emcc_args`, ever since the test
was added back in c33af78.

When actually running with `-fshort-wchar` the test fails under the
sanitizers I believe because wcslen (which is part of libc) would also
need to be built with this flag.

test/test_core.py

@@ -5680,8 +5680,11 @@ def test_utf(self):
     self.do_core_test('test_utf.c')
 
   def test_utf32(self):
-    self.do_runf('utf32.cpp', 'OK.')
-    self.do_runf('utf32.cpp', 'OK.', args=['-fshort-wchar'])
+    self.do_runf('utf32.cpp', 'OK (long).\n')
+
+  @no_sanitize('requires libc to be built with -fshort-char')
+  def test_utf32_short_wchar(self):
+    self.do_runf('utf32.cpp', 'OK (short).\n', emcc_args=['-fshort-wchar'])
 
   @crossplatform
   def test_utf16(self):

test/utf32.cpp

@@ -12,7 +12,7 @@
 typedef unsigned int utf32;
 typedef unsigned short utf16;
 
-EM_JS_DEPS(deps, "$UTF32ToString,$stringToUTF32");
+EM_JS_DEPS(deps, "$UTF32ToString,$stringToUTF32,$UTF16ToString,$stringToUTF16");
 
 // This code tests that Unicode std::wstrings can be marshalled between C++ and JS.
 int main() {
@@ -51,14 +51,16 @@ int main() {
     assert(memory[5] == 0);
 
     delete[] memory;
+    printf("OK (long).\n");
   } else {
+    assert(sizeof(wchar_t) == 2);
     // sizeof(wchar_t) == 2, and we're building with -fshort-wchar.
     utf16 *memory = new utf16[2*wstr.length()+1];
 
     EM_ASM({
       var str = UTF16ToString($0);
       out(str);
-      var numBytesWritten = stringToUTF16(str, $1, $2);
+      var numBytesWritten = stringToUTF16(str, $1, Number($2));
       if (numBytesWritten != 25*2) throw 'stringToUTF16 wrote an invalid length ' + numBytesWritten;
     }, wstr.c_str(), memory, (2*wstr.length()+1)*sizeof(utf16));
 
@@ -74,13 +76,13 @@ int main() {
     EM_ASM({
       var str = UTF16ToString($0);
       out(str);
-      var numBytesWritten = stringToUTF16(str, $1, $2);
+      var numBytesWritten = stringToUTF16(str, $1, Number($2));
       if (numBytesWritten != 5*2) throw 'stringToUTF16 wrote an invalid length ' + numBytesWritten;
     }, wstr.c_str(), memory, 6*sizeof(utf16));
     assert(memory[5] == 0);
 
     delete[] memory;
+    printf("OK (short).\n");
   }
 
-  printf("OK.\n");
 }