structured assembler for gnu as ?

[Bill Westfield]

Is there a standard implementation of "structured assembler" macros for gas?
_if, _else, _endif, _do, _while and similar? (which in general would
end up being converted to appropriate single branch instructions.)
I've found these useful using other assemblers, and I have some gas
macros that I think work, but I'd rather use a debugged and well-known
implementation than have my own version...

Thanks
WestfW