[PATCH V2] add Mac OS X support

[Jon Loeliger]

> use dylib shared lib extention
> allow to specifiy os specific shared lib link option
> Mac OS use -dynamiclib instead of -shared, -install_name instead of -soname
> and does not support --version-script
> 
> add HOSTOS macro to detect the current os you are
> 
> Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj at jcrosoft.com>
> ---
> V2
> detect dynamicly the host OS


Applied and pushed out.

Thanks,
jdl