Add new warning suppression for test_em_asm_c89 (#21583)

New versions of clang issue a new warning for this case:
error: passing no argument for the '...' parameter of a variadic macro is a C23 extension [-Werror,-Wc23-extensions]
Only -Wno-c32-extensions is needed on the new version, but for now use both to
work with older and newer clang versions.

Author: dschuff

test/test_other.py

@@ -11562,7 +11562,8 @@ def test_em_asm_c89(self):
       }\n''')
     self.run_process([EMCC, '-c', 'src.c',
                       '-pedantic', '-Wall', '-Werror',
-                      '-Wno-gnu-zero-variadic-macro-arguments'])
+                      '-Wno-gnu-zero-variadic-macro-arguments',
+                      '-Wno-c23-extensions'])
 
   def test_em_asm_strict_c(self):
     create_file('src.c', '''