readability-use-concise-preprocessor-directives

Finds uses of #if that can be simplified to #ifdef or #ifndef and, since C23 and C++23, uses of #elif that can be simplified to #elifdef or #elifndef:

#if defined(MEOW)
#if !defined(MEOW)

// becomes

#ifdef MEOW
#ifndef MEOW

Since C23 and C++23:

#elif defined(MEOW)
#elif !defined(MEOW)

// becomes

#elifdef MEOW
#elifndef MEOW