```ruby
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

require 'mkmf'
extension_name = 'atomic_reference'
dir_config(extension_name)

case CONFIG["arch"]
when /mswin32|mingw|solaris/
    $CFLAGS += " -march=native"
end

try_run(<<CODE,$CFLAGS) && ($defs << '-DHAVE_GCC_CAS')
int main() {
  int i = 1;
  __sync_bool_compare_and_swap(&i, 1, 4);
  return (i != 4);
}
CODE

create_makefile(extension_name)
```

Set march appropriately on RHEL5 32bit
user
```ruby
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

require 'mkmf'
extension_name = 'atomic_reference'
dir_config(extension_name)

case CONFIG["arch"]
when /mswin32|mingw|solaris/
    $CFLAGS += " -march=native"
when 'i686-linux'
    $CFLAGS += " -march-i686"
end

try_run(<<CODE,$CFLAGS) && ($defs << '-DHAVE_GCC_CAS')
int main() {
  int i = 1;
  __sync_bool_compare_and_swap(&i, 1, 4);
  return (i != 4);
}
CODE

create_makefile(extension_name)
```
assistant