Why does the C preprocessor need the #elif syntax at all? C doesn't have it, it just achieves "else if" by embedding the second if statement inside the else clause. But maybe that wouldn't work in the preprocessor?

    #if FOO
        foo();
    #elif BAR
        bar();
    #endif

    #if FOO
        foo();
    #else
        #if BAR
            bar();
        #endif
    #endif

I guess it works but it's clunkier.