make C# mac build use same args as in artifact builder

tools/run_tests/run_tests.py

@@ -478,9 +478,8 @@ class CSharpLanguage(object):
       _check_compiler(self.args.compiler, ['default'])
       if self.platform == 'mac':
         # On Mac, official distribution of mono is 32bit.
-        # TODO(jtattermusch): EMBED_ZLIB=true currently breaks the mac build
+        self._make_options = ['EMBED_OPENSSL=true', 'EMBED_ZLIB=true',
-        self._make_options = ['EMBED_OPENSSL=true'
+                              'CFLAGS=-m32', 'LDFLAGS=-m32']
-                              'CFLAGS=-arch i386', 'LDFLAGS=-arch i386']
       else:
         self._make_options = ['EMBED_OPENSSL=true', 'EMBED_ZLIB=true']