Doesn't compile:
MouseUtil.xs: In function 'mouse_mro_get_linear_isa':
MouseUtil.xs:14: warning: implicit declaration of function 'hv_fetchs'
MouseUtil.xs:14: warning: cast to pointer from integer of different size
Mouse.xs: In function 'mouse_calculate_all_attributes':
Mouse.xs:63: warning: implicit declaration of function 'STR_WITH_LEN'
Mouse.xs:63: warning: passing argument 1 of 'Perl_newSVpvn_share' makes pointer from integer
without a cast
Mouse.xs:63: error: too few arguments to function 'Perl_newSVpvn_share'