XaoS: fix REQUIRES, add support for x86_gcc2 secondary arch.
XaoS: fix REQUIRES, add support for x86_gcc2 secondary arch.

* lib:libgsl is neither available nor needed on x86_gcc2.
* XaoS 3.4 fails to build on x86{,_64}, even without libgsl.

nielx/haikuports,Begasus/haikuports,Begasus/haikuports,nielx/haikuports,haikuports/haikuports,haikuports/haikuports,Begasus/haikuports,Begasus/haikuports,nielx/haikuports,moochris/haikuports,haikuports/haikuports,haikuports/haikuports,Begasus/haikuports,moochris/haikuports,moochris/haikuports,haikuports/haikuports