Backport of C23's typeof_unqual in plain C18

typeof_unqual.c

#define typeof_unqual(x) __typeof__(((void)1, *(__typeof__(x) *)(void *)0))

int main(void) {
	const int ci = 1;
	typeof_unqual(ci)        i1 = ci;
	typeof_unqual(const int) i2 = ci;
	i1 = 0;
	i2 = 0;
	return i1 + i2;
}