see https://github.com/php/php-src/pull/1241 for the latest version

spoofchecker.c

// intl/spoofchecker/spoofchecker.c

void spoofchecker_register_constants(INIT_FUNC_ARGS)
{
    #define SPOOFCHECKER_EXPOSE_CLASS_CONST(x) zend_declare_class_constant_long(Spoofchecker_ce_ptr, ZEND_STRS( #x ) - 1, USPOOF_##x);

    SPOOFCHECKER_EXPOSE_CLASS_CONST(ASCII)
    SPOOFCHECKER_EXPOSE_CLASS_CONST(SINGLE_SCRIPT_RESTRICTIVE)
    SPOOFCHECKER_EXPOSE_CLASS_CONST(HIGHLY_RESTRICTIVE)
    SPOOFCHECKER_EXPOSE_CLASS_CONST(MODERATELY_RESTRICTIVE)
    SPOOFCHECKER_EXPOSE_CLASS_CONST(MINIMALLY_RESTRICTIVE)
    SPOOFCHECKER_EXPOSE_CLASS_CONST(UNRESTRICTIVE)
    SPOOFCHECKER_EXPOSE_CLASS_CONST(RESTRICTION_LEVEL_MASK)
    #undef SPOOFCHECKER_EXPOSE_CLASS_CONST
}

// spoofchecker/spoofchecker_class.c

ZEND_BEGIN_ARG_INFO_EX(spoofchecker_set_restriction_level, 0, 0, 1)
    ZEND_ARG_INFO(0, checks)
ZEND_END_ARG_INFO()

zend_function_entry Spoofchecker_class_functions[] = {
    PHP_ME(Spoofchecker, __construct, spoofchecker_0_args, 
    ...
    PHP_ME(Spoofchecker, setRestrictionLevel, spoofchecker_set_restriction_level, ZEND_ACC_PUBLIC)
    PHP_FE_END
};

// spoofchecker/spoofchecker_main.h
PHP_METHOD(Spoofchecker, setRestrictionLevel);

// spoofchecker/spoofchecker_main.c

PHP_METHOD(Spoofchecker, setRestrictionLevel)
{
    zend_long level;
    SPOOFCHECKER_METHOD_INIT_VARS;
                
    if (FAILURE == zend_parse_parameters(ZEND_NUM_ARGS(), "l", &level)) {
        return;
    }

    SPOOFCHECKER_METHOD_FETCH_OBJECT;

    uspoof_setRestrictionLevel(co->uspoof, level);
}

test.php

$checker = new Spoofchecker;
$checker->setChecks(Spoofchecker::SINGLE_SCRIPT);

var_dump(
    true === $checker->isSuspicious("latinதமிழ்")
);

$checker->setRestrictionLevel(0x40000000);

var_dump(
    false === $checker->isSuspicious("latinதமிழ்")
);