Using alias to control a test

I am trying to use the 'alias' rule to decide whether something is 
tested or not based on the OS and toolset. So I had:

alias somealias : sometest ;

alias somealias : : <target-os>windows <target-os-windows:toolset>gcc ;

in order to keep 'sometest' from being tested when gcc on Windows was 
invoked. Does anybody know why this does not work ?

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