Corrected Modelsim known functions flag error

Signed-off-by: deathwarror <deathwarror@gmail.com>
Build of corrections

Signed-off-by: deathwarror <deathwarror@gmail.com>
Added Error 21s advanced Error Message

Signed-off-by: deathwarror <deathwarror@gmail.com>
Corrected Error 21s error number for error message

Signed-off-by: deathwarror <deathwarror@gmail.com>