Suppression of built in pre/post randomize functions for -Wunused-class-method

[jcurtiss8086]

This is a minor corollary to the rand-var change made for #1678

The built-in pre_randomize()/post_randomize() functions get called automatically during randomization so usually won't have any direct-references in code. Can these two methods be auto-suppressed for -Wunused-class-method? Otherwise, the new warnings are looking good for the first repo I've run through. Thanks!

unused-class-method.sv:4:19: warning: unused class method 'pre_randomize' [-Wunused-class-method]
    function void pre_randomize();
                  ^
unused-class-method.sv:7:19: warning: unused class method 'post_randomize' [-Wunused-class-method]
    function void post_randomize();
                  ^

class C;
    rand bit a;

    function void pre_randomize();
    endfunction

    function void post_randomize();
    endfunction
endclass

[MikePopoloski]

Fixed in 86cf7ae