Goa: build working libraries for arm_v8a

Hello Sebastian and all

After a lot of trail and error, I'm finally able to build shared libraries for the arm_v8a platform. My test component (wasmedge) runs successful on my iMX8 device :-).

It turns out, that when using gcc to link libraries the argument `-shared` passed by cmake seems to behave differently between x86_64 and arm_v8a.

In the arm_v8a case this needs to be prefixed with `-Wl,`.

I have changed share/goa/lib/build/cmake.tcl to add this to the linker flags for libraries on all platforms. This is somewhat redundant, and there might be a better solution, that I currently can't see. I'll be happy to improve during the code review.

Regards, Pirmin