autoconf: make sure 'restrict' keyword is always available
autoconf: make sure 'restrict' keyword is always available

rabbitt/libusual,ifduyue/libusual,ifduyue/libusual,mgjv/libusual,markokr/libusual,markokr/libusual,ifduyue/libusual,markokr/libusual,markokr/libusual,rabbitt/libusual,rabbitt/libusual,mgjv/libusual,mgjv/libusual,rabbitt/libusual,mgjv/libusual,ifduyue/libusual